A lot of people here bitching about people who only play themselves like Tom Cruise but when the role is written for your personality it still works. And if you're going to bag actors for only playing themselves you have to put Patrick Stewart in that group. Because he can only play one role (in various forms)...
But there's also -
John Malkovich a stage actor who always over-acts on film, yet he has been a couple of good films so there's...
Adam Sandler a 'comedy' actor who is never honest, or funny, but he was good in Punch Drunk Love so there's...
Nicolas Cage is incredibly hit and miss but he's been great a few times...
Dana Carvey terrible actor but is hardly in movies so I'm going for...
Either Halle Berry (just terrible), Jessica Alba (zero depth, cannot play darker roles) or Paul Walker (so funny in Fast & the Furious he's almost good).