If we’re talking solely movies that are on par with or better than the previous ones (i.e. not a significant step down), then the only ones that come to mind are as follows:

Revenge of the Sith

Jurassic Park III (not really a trilogy since they’re all standalone)

Return of the King (I saw it once ages go, but I’m pretty sure it was on par with the others)

The Last Crusade is borderline case because it is a step down from the other two (it’s a bit too derivative of Raiders in some ways), but it’s still really good (also not really a trilogy)

I haven’t seen Back to the Future III in ages but I think it might hold up

What about game trilogies? I haven’t played it yet but I hear Mother 3 is great. Super Mario World is pretty beloved. Do people like Metroid Prime 3? I’m not a Metroid fan so I wouldn’t know. What’s the verdict on Donkey Kong Country 3?