I bought this game yesterday...
All that needs to be said is in one evening to myself I leveled my "Brick" to level 16. Very fun and addictive.
I can't wait to try the game in co-op, but since none of my friends at school will probably be interested in playing, I'll have to go ahead and get XBox Live and enjoy it that way. I'm content to just play through the game once or twice on my own first, though.