Acting- what makes a good role?

Acting is one of the integral parts of movie-making. Bad acting can sink a movie faster than a leaky lifeboat (Leaky lifeboats!?). Good acting can sustain a film, even define it. What makes good acting though? It's really a matter of opinion. Of course, some people have a better opinion than others.
To me, acting is in in the nuances. The way an actor delivers a line for emphasis, their voice fluctuating where it regularly should not. The way they walk or move. The more subtle the detail, the better. Because in all honesty, who really twitches or mutters in an over-obvious way? If an actor has to do too much it is too much. Then again, some actors thrive on overacting. Mostly comedians. Or Jimmy Stewart.
What kind of roles are the best kind then? Well, if you ask the Academy it's the kind your average joe would say is good acting. This means playing the mentally or physically handicapped, someone gay, or a famous figure. Don't get me wrong, these roles are challenging. Their just too obvious. I say the best kind are the ones where an actor can build on a fictional character who has the kind of issues you may not know but notice if you look well enough. A drug addict. A person who's spouse is cheating on them. A person with social anxiety disorder. Think of how hard it is to convey the emotions requisite of a person who's problems are under the surface. Do you wear your problems on your sleeve?
When I watch Sean Penn act, I find it very smug. Almost like he knows he's got some meaty, meaningful role. When I watch Tom Wilkinson, I see an actor with versatility. It's personal opinion. I will argue my opinion is superior to yours, but I will respect that you have an opinion.