OK, how about ones that will cause arguments?
I vote Clint Eastwood.
People talk about him being such a good actor, but it seems to me he just scowls his way (the AME way) through each film.
Eastwood is a star in the old vein, like John Wayne. Doesn't mean they weren't good actors, but they were/are limited actors. Like each of Wayne's roles was pretty much John Wayne, each of Clint's roles is pretty much Clint Eastwood. If you like those personae, you're gonna like the actors. If you don't, they are a disaster. I will admit that both have grown on me and I enjoy their work, although neither will make me forget Spencer Tracy. YMMV. Also, I think Eastwood makes some very good movies, along with some turkeys.
My vote for the most overrated actor is the universally acclaimed Sean Penn. He's not horrible, but IMHO, he has never earned the accolades he's been given and, frankly, he bores me.
