Skyward Sword brought down Zelda. Other M brought down Metroid. Super Paper Mario brought down Paper Mario and Sticker Star crapped all over it. Pikmin 3 brought down Pikmin. Dang, Nintendo's really in a slump, huh?
I might have to say Smash Bros. I know a lot of people didn't like Brawl as much, but I'm a casual and loved all the extra features and characters and stuff. Though the next one will probably bring it back down by not having a story mode, so...dang. They need to get it together.
Currently playing:
Bloodbath Paddy Wagon Ultra 9