I'm going to say it right now, Team Fortress 2 is terrible on single player.
As far as best, I'm going to have to go with Mass Effect 2. OK, so the control scheme wasn't quite up to par with most modern Third Person Shooters, but it had amazing writing, an interesting story, characters who I gave two shits about, AND competent gameplay. Bioware effectively kept everything I loved about the first one (you know, besides half my party), and rounded out the gameplay to be playable. It really resonated well for me, but I suppose if ME1 managed to be my favorite game up until ME2 came out, then a positive re-working of the combat system and leaving everything that was good good would manage to make an impression.