Have a few hundred hours in the game, still play fairly regularly, come back in force for each event. Toss a $10 their way at the end of each event.
Overwatch is the only game I've EVER had where I've paid money for microtransactions, which by default I guess makes them the 'best microtransactions ever', which I understand to some (and before overwatch, me) sounds like "the best plague ever".
Some key things about what Overwatch does:
-Cosmetics only, zero pay-to-win unless you consider looking pretty awesome as winning
-Large variety. 24 characters, most having 70+ items each.
-Pretty great art design for those rewards
-Only a single box with a straightforward method of acquisition, and a single currency. If there was like a 'platinum box' and a 'gold box' that all had different requirements, it'd be kind of whack. I also don't like that Heroes of the Storm has 3 different currencies or whatever.
-Well-tuned reward drip. Not so frequent that they don't feel special, not so rare that they feel unattainable.
The biggest downside is the duplicate aspect of the system, but I think the elegant simplicity of the single loot box, the production values around the opening animation and the rewards, and the frequency with which they are earned manage to outweigh that for now.