+1
This is really a complicated question that likely needs some complicated answers. I'll do my best here:
Highly rated and yet still somewhat UNDERRATED: Russel Crowe. <----The performance in A Beautiful Mind still does not get enough acclaim, and him being robbed at the oscars was a just a crime. To be able to pull that role off and not "see" Russel Crowe but John Nash was astounding to me.
TOTALLY OVERRATED, but can make a good movie: Kevin Costner. The guy has such a cardboard expression for nearly all of his emotions, it's pathetic to me. My golden retriever can summon more expressions on demand.
MOSTLY OVERRATED, and no one agrees with me: Meryl Streep. And because no one agrees with me, I'm not getting into it.
CRAZY HIGHLY RATED JUSTIFIABLY: Jack Lemon. All the proof I need: Final scene in Glenngary Glenn Ross (a film otherwise dreadful to me).....He managed to pull off showing a guy in terror at not being able to maintain the right responses to cover his obvious mistake of giving away that he knew that Kevin Spacey was making things up.
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Rules: When women have a poet, they want a cowboy.
When they have a cowboy, they want a poet.
They'll say "I don't care if he's a poet or cowboy, so long as he's a nice guy. But oh, I'm so attracted to that bad guy over there."
Understand this last part, and you'll get them all.