When I see a performance in a movie, I want the actor to get across why their character is doing what they are doing.
I am all for ambiguity: human beings often have lots of competing, overlapping, and even contradictory reasons for doing something, so I especially appreciate it when an actor can get mixed motivations across all at once.
If the character's motivation has to stay hidden (as with Julianne Moore's performance in Neil Jordan's version of The End of the Affair), then (a) I want it to make sense in retrospect once the mystery is solved and (b) I want to be able to speculate meaningfully about the pre-solution parts of the performance.
When I see a performance in a movie, I want the actor to expose the emotional state of their character.
Maybe expose is the wrong word, but I'm wary of getting too poetic or too sappy. I'm thinking here of something like Jennifer Connelly's performance in Dark Water: she doesn't build her character like the supporting actors do in that movie, she's not especially convincing (nor is she especially unconvincing) as a young working, single mom. But she opens up to the camera and radiates vulnerability.
Of course, I don't like having to use a word like "radiates" to talk about this - too poetic again. More specifically, she has an expressive face and she's comfortable enough in front of the camera to let it pick up all its subtle shifts.
When I see a performance in a movie, I want the actor to impress me with their skills.
We are talking about performance after all, and showing off what you can do is a big part of that.
Skills is a big category, though. It can be actory skills - Kevin Spacey's inventive line readings in The Usual Suspects or L.A. Confidential, Daniel Day-Lewis's physical work in My Left Foot - or it can be showier, song-and-dance-style skills - Jackie Chan's highly choreographed stunts and fights in Project A, Steve Martin's physical comedy in All of Me.
When I see a performance in a movie, I want the actor to create a character (or at least a moment) I might recognize from life.
I want to be convinced. Like with Ricky Gervais as David Brent in The Office: he obnoxious like people I know in real life are obnoxious, not charmingly obnoxious like a lot of TV characters.
Five: Swept Away
When I see a performance in a movie, I want to be charmed.
Moviemaking isn't necessarily that much fun. Work is work and while I don't have any extra sympathy for actors (who are, after all, probably getting paid to do what they love), I do recognize that the process can be just as much a pain in the ass as many other jobs.
But when I go to the movies, I don't want to have to think about any of that. So, when I'm watching Will Smith in Enemy of the State, I don't want to start thinking about what a drag it must be to have to run around one of these big budget action monstrosities: I just want to admire his poise and sense of humor.