Many critics agree that actors and actresses like Sean Penn, Johnny Depp, Tom hanks and Nicole Kidman are "third dimensional" performers because they are able to provide more passion than their scripts wrote. Although I am not sure what "third dimensional" means, but I think Tom Hanks' acting touches people easily especially in Philadephia and Road to Perdition. Do you have any "third dimensional" performers in mind and would like to discuss them?

I agree with all the ones you listed. Some that I can think of that you didnt list are Jack Nicholson, Meryl Streep, Julianne Moore, Renee Zelwegger, I'll stop there and leave other people some to post.

It think "third dimensional" or "three dimensional" means having the ability to transform yourself into any character, no matter how close it is to your acutal self. It is the ability to put yourself in action roles, romance roles or any kind of roles. To fit this category, you have to be in a variety of movies so people can see you in different rolse. A person who wins the oscars for best actor once doesnt neccesarily fit this.

Well, at least those are my personal thoughts on the subject.

Tom Cruise, Dustin Hoffman (for his brilliance in "Rain Man"), Cuba Gooding Jr. (Not great but was exceptional in a couple movies), Morgan Freeman, Tim Robbins, Mel Gibson. Those are couple off the top of my head.

How 'bout:

Anthony Hopkins (esp. in "Silence of the Lambs")

Samuel L. Jackson (esp. for his brilliant performance in "Pulp Fiction")

Gene Wilder (In "Willy Wonka and the Chocolate Factory)

Oh, and of course Nicholas Cage! (Mainly for his amazing duo performance in "Adaptation")

Even though I've only seen her a couple times, I think Kate Winslet is a great actress from Finding Neverland to Eternal Sunshine of the Spotless Mind to Titanic.

how do guys decide that one is a "great" actor/actress? Just because critics say so? (well, of course, peopole can't deny their critiques) What if you have to sit in a movie theater, without any previous knowledge of an actor/actress, how would you evaluate his/her performance? I really don't understand sometime how critics decide that one is a "great" actor/actress

Well, that is an interesting point. I wander if our thought on who is a good actor or not is affected by the public, peers and critics ect. Well, at least for me, I try to go into a movie without thinking of the meta-score in recieved so I can decide for myself how good the movie is. But, I am sorry to say that really the meta-score does affect my mind on what is good or what is not. That is for movies, for actors and actresses, Im not exactly sure. I know it probably has some affect on my mind and who is a good actor ect.

Oh, an obvious one Bobby De Niro, and you can add Al Pacino too.
And on the question of what makes a "good" actor, if you forget that your watching an actor, then he/ she is good.