I'm not a fan of Captain Kirk on Star Trek, but I like the other main characters, Mr. Spock and Dr. McCoy. It's impressive how much Spock seems like a legitimate alien, and not just a human with putty on his ears. As for McCoy, I like him because he's more or less the only normal person on the show. Spock and McCoy play off each other very well, and I think it works so well because they are both extremely smart.
I have no real opinion on Mr. Sulu. I know George Takei has made a career out of the role, but he is a really unimportant character. He's more like an extra who shows up a few times than a reoccurring character. I am still unsure as to what role he fills on the ship. It seems like his particular field of expertise changes, depending on what the script calls for.
I can't understand half of what Chekov says.
Scotty is an okay character. It's interesting, because he's a generic tech guy, and in no way does he match up with our modern conception of "generic tech guy". He generally doesn't do much besides exposition, but on the occasions where he steps up and takes control of the ship (since the captain and first officer are constantly abandoning the ship to enter dangerous situations), he does a fair job.
Lt. Uhura is a pretty awful actress. She does a blank stare all the time and talks in a monotone. When she did actual acting in the "Mirror, Mirror" episode, I was shocked. In her defense, though, none of the women on the show ever seem to have good roles. It's very much a male-dominated show.