Cross Edge. Battle system is the best I've played this gen, there are a ton of characters so you're bound to end up with a party you love, the music is great and there's plenty to do. Synthesis and Item Customization actually helps you make it through some of the challenges too. It's not just there to go from beating the enemies to obliterating them.
For me, it would be Psychonauts. The voice acting was great, the gameplay was unique, the humor always made me laugh a little, and the story was a lot more deep than you'd think. Though, in recent years, I've seen it pick up steam.