I'd have to go for Far Cry 2, and mainly because I paid full price for it and expected so much from it.
Driving endlessly around the African countryside got boring fairly quickly, but I would have been fine with it if it wasn't for those ridiculous respawning checkpoints. I mean, I wipe out a checkpoint completely, then go round the corner, realise I've driven the wrong way on the map, do a U-turn and head back up the road and they're all back and all super pissed! It really got to the point where I just lost the will to play the game anymore. It wouldn't even have bothered me so much if I could breeze through them and only receive a couple of bullet holes in the side of my vehicle, but NO! When I drive through at top speed, they always managed to catch up with me in their rocket powered super jeeps! Strange considering the last time I offed their stupid asses, I took one of these miraculous vehicles but unfortunately I just didn't have the special touch to send it into hyperdrive. So they'd catch me. And they'd shoot the everloving shit out of my car. And I'd have to get out and fight them. And then I'd take their car. And then I'd hit another checkpoint two minutes later and the whole forsaken dance would start again.
To be honest, I don't think it would have been so bad if you could even slow down and use the checkpoints like they'd intended, with a dude checking your papers and what not. At least if you're not a wanted rabblerouser in the area. But I found, on my attempt to initiate this, that I just got an AK-47 clip emptied into the side of my face instead.
As a consequence I played very little of the game, which I find to be a great shame as it's not often that a game comes around that I really want to play.