I've never played BF:BC so I can't comment on that title, but if your decision comes down to COD4 or WAW I would honestly recommend COD4. I have both and I enjoyed COD4's online and single player much more in contrast.

Mass Effect and BioShock had a great story, HL:2 with the Orange Box is also pretty good.

Ninja Blade might be worth looking into based on your criteria.

COD:WAW on veteran, nadestorm.

I love both games, but Mass Effect is more immersive in my books.

If you're willing to spend the money on it despite MW2 being slated for a November release, I'd say they're decent enough.

Broadcast and Creek really stand out, Chinatown is also okay.

Mass Effect, love that game.