All time favourite/greatest sequels

Some games are called classics for a reason - they bring about innovations in game-play and graphics that gamers will appreciate for years. One advantage that video games have over cinema is that video games sequels are more often than not a genuine improvement ("Aliens" and "T2: Judgement Day" notwithstanding, of course ) and sometimes, somehow, surpass the original games in quality and enjoyment. Which video game sequels do this for you?

Super Mario Land 2: Six Golden Coins
Donkey Kong Country 2: Diddy Kong's Quest
Banjo-Tooie
Jak II and Jak 3
Spiderman 2 (same with the films)
Tony Hawk's Pro Skater 4 (Controversial, I know)
GTA: Vice City (Technically a prequel, but definitely topped GTA III for me)
Super Mario Galaxy 2

Just a couple at the moment:

Spyro 2 and 3: Both Spyro games improved in the original a lot and made it a lot more enjoyable. The third's one of my all-time favourite games.

Phoenix Wright: Trials and Tribulations: Best story of the trilogy hands-down, although Justice for All gets kudos for an amazing ending case.

Streets of Rage 2 for the win!!!!!

I 2nd Streets of Rage 2
Sonic 2
Resident Evil 2
Just Cause 2
Ratchet and Clank : Locked and Loaded

and a couple that didn't quite get it right

Crackdown 2
Mass Effect 2 (I enjoyed the micro-management of the original)