I played a lot of Advanced wars around September of last year and it's easily the best of the series. There's tons to unlock, tons to play around with, and I imagine most people will play the hell out of it well before they unlock everything. It was the game that kept me sane during my biannual month of doom that is the beginning of the school semester. I think the only reason I stopped playing it was because I wanted to play something else in my free time when I started to get more.
Metroid Pinball is a lot of fun too. Aimee ended up playing it a lot more than I did because she's really good at pinball games, but I completely enjoyed it. As pinball games fun, it's way up there.