BC2, TF2 (... no, wait: pretty much every single valve game). Have to agree Deus Ex was also but depending on what type of "modern" the OP was referring to (is it a modern/post-modern setting, or released recently?), it may not count. Lost interest in CoD4 after awhile (losing my cd-key didn't help). And even though MW2 was fun and all, something didn't click after awhile, and the lack of dedicated servers eventually got to me.
Borderlands was amusing, and FO3 was nice once modded (extensively).
No offense to Halo players everywhere, but... no. And Arma 2 just didn't feel right, something felt awkward about it to me.