I'm loving this game. I had it pre-ordered at Gamestop and was planning on picking it up at midnight with my DSi but I walked into Best Buy this morning and saw it sitting in the DS section. Took it up to the cashier and bought it and I was surprised that a notification didn't come up on the computer when he rang it up since it's not officially supposed to be out until tomorrow (that happened to me when I tried to buy Burnout Paradise 2 days before the release day).
So far the game is crazy addictive. I've pretty much been playing it all day and it is quite challeneging but not in an annoying way. Awesome job Nintendo!!!