He wasn't a bad actor. He didn't ruin movies. I wasn't (always) embarrassed for him when I watched him act.
Gridlock'd is the only decent movie he was in, but Juice is his best performance. When he points the gun at Raheem and says, "I'm not playin", that's his best moment on film.
It's hard to pick his worst moment. There are many bad ones. He wasn't terrible in Poetic Justice, but it's one of the worst movies I've ever seen, so it counts against him. It's not as bad as Bullet, though. He'd clearly lost the love by that point. Horrible performance. And Gang Related, oh boy. If you can sit through a movie where Tupac's name is Rodriguez and his partner is Jim Belushi, congrats, you like Pac more than I do. Dogshit.