It would be a bit easier to recommend games if we knew a bit more about your particular tastes in games. Still, I think i can point out a few.
For a good free-roam action/ adventure game pick up Daxter, starring Jak's furry sidekick and takes place between the first 2 Jak & Daxter games.
If you want something a bit more original grab a copy of Loco Roco. This game has a very quirky feel to it (as did the Katamari games) and can be somewhat addictive.