Tom Cruise. To me he's the quintessential "movie star" but not great actor. Never really been moved by any of his performances sans Les Grossman
Keanu Reeves. I like Keanu, and I like a lot of his movies, but his acting chops are a notch higher than Freddie Prinze Jr. He is the Anthony Kiedis of acting.
Liam Neeson. Some great work but way too much playing the same god damn role over and over, making himself into a caricature. I think there's a line where you can be a good/great actor, but if you keep taking the wrong roles it eventually effects your legacy. And I know his wife died and it changed his goals or whatever but hey man I can only judge you by the roles you play.
Also - Joaquim Phoenix. Joaquim Phoenix is a Paul Pierce who is routinely graded as Kobe Bryant. and this is coming from a Paul Pierce fan. Dude is a great actor, he's just not on the tier people routinely put him on, not for me anyway.