I don't wanna sound so down on XC3 which I have enjoyed a lot, but the other games absolutely captivated me. I also haven't quite finished XC3 yet, I'm in chapter 7 waiting for the DLC with a new character and challenge arenas before I continue, so maybe the ending will change my feelings about it.
Story
1. XC1 - A perfect and complete Hero's journey that starts in a little town, spans an amazing world of adventure and ends in a cosmic finale.
2. XC2 - While I can't say I've ever been bothered by women having boobies, the other anime tropes like sappy emo villains and exhaustingly long flashbacks explaining their motivations really made the story an eyerolling chore at times. But there were many other wonderful story elements to balance that out. Great moments of action and humour, dramatic setpieces, some wonderful sidestories for your many rare blade characters, awesome late game revelations that contextualize the shared universe of Xenoblade games and a literally perfect ending make it one of the better Xenoblade stories despite the crappy parts.
3. XC3 - It's really good. Some great moments and a few lame ones but I still haven't quite finished it so maybe it can change my mind with a really good ending. From where I'm at now, it looks like the burden of having to tie together other Xenoblades, which they've certainly done an admirable job of, has led to a less interesting story than when Monoliftsoft just tell whatever story they want.
4. XCX - A fantastic premise is wasted by not even trying to tell a story as grand as the other games. It still has some great moments and I love it for what it is, but the story is not where the developers put their energy and it shows.
Characters
1. XC1 - There's something just perfect about this crew. Shulk the bright youngster having to grow up quickly while wrestling with revenge, Reyn the living meme, Dunban the war hero, everyone is great.
2. XC2 - While your crew aren't quite as perfect as XC1, with Rex being a weaker protagonist and cringe emo villains being the most obvious weak points, the game has a rich abundance of weird and wonderful characters because of the rare blade system. You'll also find that a love for the main cast will just creep up on you throughout the course of the game. Plus other great Xeno characters from different titles are in this game in some form, including Shulk, Fiora, Elma and Kosmos.
3. XC3 - They're good, really good even but while the cast are likeable they still don't have the impact of XC1 and XC2. For example Lanz is more than a Reyn clone, he's established as his own person with his own traits, but he's still kind of derivative of Reyn, a big beefy guy yelling at Nopon and calling them furballs. While the hero system does add to the game with cool characters like Grey, they're not as many and not as weird and wonderful as the rare blades in XC2. The villains are the worst of all though. If the villains in XC2 are cringy and anime, at least they have characterization. With some notable exceptions, whenever I'm listening to a Moebius give a long winded, hamboned speech, I feel like there's absolutely nothing to that character at all. They're just there to give that empty speech and turn into a monster so I can kill 'em.
4. XCX - They're fine. The main cast have derpy faces but I don't hate any of them except Tatsu. There are some really cool looking character designs among the villains but this is a make your own hero game with less character development than other Xenoblades.
World
1. XCX - All Xenoblade games have great environments but planet Mira is top of the class. Flying around its vastness in your mech makes exploring incredible environments like Sylvalum or Oblivia a joy.
2. XC2 - This game has some truly excellent locations like Tantal and the Urayan titan but it's also the rules of how XC2's world works that make it such a great world. Things like the different nations and cultures existing on the different titans that roam the cloud sea, and how blades are made of data and so characters from other games can be bonded to a driver in a way that makes perfect sense and fits the rules of the world.
3. XC1 - The extreme care put into crafting the perfect world for an adventure across the bodies of 2 enormous titans led to beloved locations like Gaur Plains and Satorl Marsh. The constraints of the hardware it was originally designed on are evident though.
4. XC3 - It still has great environments, it's a Xenoblade game. But so many of them are connected to/referencing XC1 and XC2. I understand the story purpose for this, but isn't it better when Monoliftsoft just go completely wild making original locations? Also, it's thrilling when you first find the huge ocean you can explore, but ultimately it kind of boils down to a lot of empty space between some small areas you'll visit once and 6 or 7 moderate sized locations to do things on.
Gameplay
1. XCX - Crazy customization to the extreme limit of fun OP brokeness. You can set up your character in all sorts of weird and wonderful ways, go solo against gigantic bosses, it's awesome. The overdrive system is also another amazing chain attack-esque mechanic with its own cool benefits, one that doesn't even require you to stop the action so you can use it in multiplayer mode. Also the game doesn't turn into a blurry mess during intense combat the way XC2 and XC1DE do on the switch, and you can fly around in a frikk'n mech yo.
2. XC2 - Yes, everyone hates gacha, yes the game explains its systems very poorly, but once you DO understand them, combat is a delight. It feels so amazing to take on massive bosses with this admittedly broken tool set, evading huge attacks at just the right time, healing your party with a massive AoE super move and getting crazy damage with fusion combos. The orb system is another great variation on the chain attack mechanic too. And I like upgrading more and more power using the weird challenges in each Blade's affinity charts.
3. XC3 - Very high levels of customization and a truly excellent new iteration of how chain attack works aside, I'm feeling a little underwhelmed by XC3. I still like fighting big monsters in it but...I don't know, it's like they tried really hard to balance things but ending up still having broken mechanics, but the new broken things might be less fun than the old broken things. Or maybe hard mode wasn't a good choice for a first playthrough. I had some really intense, exciting battles in the early game on hard mode, but in the later game the thing that's making hard mode hard is just me wanting to level up my characters in new classes. If I switch them to their best classes it's no trouble to take down the monster I'm fighting but I also lose the benefit of them gaining class points in the classes I'm trying to level up. On the plus side, elite monsters are a great addition to the series, providing a challenge somewhere between a regular enemy and a unique boss monster, and being able to fight in water is a huge step forward.
4. XC1 - I feel bad putting Xenoblade 1 at the bottom because its gameplay really is excellent. Other games added to and improved on many of its systems but some cool things are still mostly Xenoblade 1 only, like Shulk's visions of the future. It also has its own great way of doing chain attacks where you build your damage multiplier with moves of the same colour, although it does have a problem hampering fun where you have to get pretty far into the game before you can do many rounds in a chain attack. It's also really cool how each character's build and personality suits their fighting move set, something lost by more customizable games such as XCX and XC3 and another example of how everything in XC1 fits together tightly, like how the aforementioned visions of the future are very significant to both the gameplay and story.
Music
1. XC1 - Excellent music the whole way, from the title screen to the locations you explore to dramatic story moments and battles. Gaur Plains perfectly captures the sweeping feeling of adventuring in a massive open area, just like how Mechonis Field captures the funkiness of exploring a weird alien robot world, or Fallen Land perfectly captures the feeling of being lost in a new world while walking along a beach at sunset. Engage the Enemy is perfect background music to intense dramatic scenes, and You Will Know our Names is still the best unique monster battle theme... although XC3's unique monster theme is so good you could call it a tie.
2. XC2 - The game deserves this spot for Counterattack alone, the most hype background music to ever punctuate Jrpg drama scenes. But it has tons of other great songs. I actually like the soaring feeling of adventure provided by the Gormott theme even more than Gaur Plains, and other exploration tracks like Mor Ardain, Kingdom of Uraya, Tantal and Yggdrasil are all totally amazing. The only thing holding XC2 back is the battle themes aren't quite as awesome as the other games.
3. XCX - While XCX does have some of the best tracks in all of Xenoblade, it also has some of the worst. So while I might love environment tracks like Oblivia and Noctilum, battle tracks like Wir Fliegen and Uncontrollable and powerful emotional tracks like Codename Z and The Way... I have to acknowledge that you're going to be listening tracks like the very...experimental New LA theme a lot of the time when playing the game.
4. XC3 - I feel bad putting XC3 here the same way I felt bad putting XC1 last for gameplay, because XC3's music is great. It has some really hype battle music like You Will Know Our Names Finale and the Moebius battle theme. But the exploration music isn't quite sticking with me the way it does in other games, I just don't seem to remember any of it. I'm wondering if maybe the areas are too small or something? If I look up the theme music to Ribbi Flats, it's good music, but I just don't feel like I'm ever in Ribbi Flats for a long enough time for it to get stuck in my head so it doesn't seem memorable to me. Meanwhile the largest environment of the game, Erythia Sea, has great music that I do remember.
Overall
1. XCX - It's a weird one, no denying it. As hype as the struggle for human survival is, with all those epic battles set to badass music and cool weird aliens everywhere, it all amounts to zero character development and a mind trip cliffhanger ending. well...There's a sense in which XCX is a game that begins at the end credits screen. That's when you begin pimping out your mech's arsenal so it can be a boss 1-shotting machine. I can honestly say the endgame of powering up, flying around exploring planet Mira's vast environments, tackling every sidequest and beating up every overpowered tyrant left me just as emotional when it was time to say goodbye as any game with a strong cast and story.
2. XC1/XC2 (Tie) I originally gave the edge to XC1 here, but the more I thought about it, the harder it got to say XC1 is better than XC2. XC1 is a game where all its pieces fit together perfectly, from the way music matches each location to the way character's moves fit their personality, so in a sense it is better. XC2 is a game with a ton of problems, from gatcha to tech problems locking people's games, and hammer class sucking, and those field skills everyone hates, and Rex being a little weenus and tedious flashbacks, and so on. But taking the good together with the bad, XC2 has the most good stuff in it of any Xenoblade, in terms of quantity. It's a monster of game jam packed with features and content. There are way more rare blades in XC2 than there are heroes in XC3, and they have more personality too. There's awesome arena challenges, there's beloved characters from other games included into the game along with their music and mechanics, such as Shulk's vision's and Elma's overdrive. And just think of all the things you can do with Poppiswap. Plus there's Torna. That's an entire small game and the richest bit of DLC in the series thus far. Hopefully XC3's DLC content will be just as chunky.
3. XC3 - I'm on chapter 7, waiting for the DLC with robot girl Ino and battle arenas before I continue and see the rest of the game, so perhaps my feelings will change but right now it's a great game that I like a lot. However, every other Xenoblade has been a treasured experience that's very special to me, so this is a huge step down. I don't even know how to explain it, but I feel like making a title where they connect the other Xenoblades together is just not as entertaining as when Monoliftsoft make a totally new game or even a totally new Xenoblade game without such constraints.