Games you got 100% on and was it worth it?
No need to list them all, a few choice ones will do.
Jet Set Radio
60 Hours
Waste of time. Even with all the Graffiti Souls, you can never go and redo your Tags (unless I'm missing something-used copy no manual), which makes them pointless. The unlockable characters aren't too different and give no real reward.
Project Gotham Racing 2
300 Hours
Definately worth it. 4 of the 5 unlockable cars (Delphino Feroce, Merc CLK GTR, Porsche GT1, TVR Speed 12) are either completely dominant in their class or not far behind. Took a lot of time to do it but well worth it.
Advance Wars 2
+-50 hours
Makes a huge difference in the game, giving you the mammoth Tanks (Strongest tank in the game) and characters that have the best special abilites/coolest specials.