From my games, we have trauma center second opinion which is only one player but new blood has a co-op mode which is cool.
we have big brain, it's fun, when we pick it up.... DON'T get Alien Syndrom unless you're diehard fans of the retro game. Super Mario Galaxy is a beautiful game but the co-op pretty much sucks. it's good to teach your children how to play while youre the useless second player though
wii play has some fun stuff, but not like all day every day fun
my girl likes to sit and watch me play zelda(hehe)
we've reserved Mario Kart too....
looks like i haven't been much help, but maybe you have some ideas of what NOT to get
I really enjoyed the baseball on wii sports, if you know of any fun baseball games that take advantage of the wii's controls, please let ME know!!!