One major downgrade from the first game is the opening to Revenge of the Sith.
In the Skywalker saga you don't even play the flight towards Grievous's ship which is odd considering they've added so many flight based missions in.
from what I played so far the whole game can't really match Complete Saga. I think Traveler's Tales should go back to the roots of the Lego games. modern Lego games fake too much complexity, yes I said fake, because the complexity added is mostly just cosmetic and doesn't and depth to the gameplay.
Lego Star Wars 1, 2, Complete Saga and Lego Indy 1 were just as deep in terms of actual gameplay, but they were more focused on the basics of what makes the games fun. they were really intuitive to control, easy to pick up, uncomplicated to hop in and out of coop and because they didn't have any Splitscreen features yet (later lego games implemented that splitscreen feature that splits the screen once you walk too far away from eachother) and so the gameplay was way more straight forward.
I really think not a single Lego game that came out after Complete Saga was close to that game's quality (also one of only 2 Lego titles that have online Coop btw.). Lego Indiana Jones, which released a year after Complete Saga, was on the same level I would say as the standalone Lego Star Wars 2 tho, so not far off, and Complete Saga is better simply by the fact it has about 2x the content and it's Star Wars
BUT, Skywalker Saga is the best Lego game IN A LONG TIME... it trimmed down the gameplay where it mattered the most again, and that is that it went away with all the ability wheels every damn character started to have where every character had like 9 different abilities you had to switch between every 2 seconds, so thankfully they got rid of that shit.