From reading your question you seem to be in one of the same ruts that I was in previously with games. Personally I have found tons of great games on Steam lately from non-mainstream publishers. Also as I have gotten older it has become harder for me to appreciate mediocre games and instead I look for games that don't stick to the norms.

Some great examples that I can think of off the top of my head are as follows, and broken down by category:

Unless otherwise stated, these games are all available on Steam.

Strategy:
Braid
Machinarium
Worms Reloaded
Zen Bound 2

Adventure:
Darksiders
Lost Planet 1 and 2

Action:
Deus Ex: Human Revolution (Comes out Feb 2011)
Beat Hazard
Brink
Killing Floor
Smashball (Free!)
Trine
VVVVVV
League of Legends (www.leagueoflegends.com)

RPG:
Torchight
Freedom Force
Dragon Age Origins
Star Wars: Knights of the Old Republic 1 and 2
The Witcher 2: Assassins and Kings
DeathSpark
The Ball
Shank

Misc:
Garry's Mod

I hope this list helps you find some games that you can enjoy. Most all of them are more of a casual style that way you don't have to sit down to play it all at once, though you may be inclined to.

One way that you could do this is to use something such as AutoHotkey which will allow you to filter inputs and send them to a specific application to allow both of you to play at once. It would require the use of a more glorified script like those written for multiboxing in WoW or other games. Check out autohotkeys site and look around for some premade scripts. Their language has a very straightforward API with a knowledgable fan base, I'm sure you can come up with something.