Eh, I consider most games to be a grind if I start going for full achievement, but I've very rarely found a single game a chore. I know everyone goes on about how you have to do hours of repetitive fighting to level up so you can face monsters in say FFVII or FFIX, but I got through both those games and only really needed to go out into a field every so often and smack some bitches when a particularly hard boss fight was coming up, so it never felt chorish, just like a nice distraction to work on some tactics for more important fights.
I guess my three biggest concessions to this law are [PROTOTYPE], GUN, and Gears of War 1
[PROTOTYPE], possibly because I just glutted it all in a weekend, started to feel like a chore sometime around when I had to run around smacking Elizabeth Green's massive monster form, all over town, with the anti-virus canisters and the troops who seemed to think one man in a hoody was more of a threat than the gigantic phallic tentacle monster rising from the ground and slaughtering them. Eventually I just sat back and let EG kill all of them, then went in to stomp her.
GUN, the final boss is a *****, no more need be said.
Gears of War, the only game in my entire gaming history that I have given up on because the final boss was suck a trial of luck instead of skill. Dodgy controls, bad AI, ridiculously overpowered attacks that even when I could figure out the patterns to they still seemed to sometimes come at random just to fuck with me, a legendarily stupid AI partner, a nigh-on impossible to hit bad guy with oodles of health and setting that makes no sense given that the train we were on is supposed to at some point reach a destination, but I managed to stay alive for 45 minutes and we didn't even up anywhere. I consigned it to the suck pile and have ignored the series since.