For me, the most important thing at a golf course I play is the greens. If they don't roll well, it matters not how the rest of the course is, you're going to be left with a bad taste in your mouth.
Second, I want level tees and if I'm in the fairway, I want a decent lie, for the most part.. It's such a simple thing to ask for yet amazing how often you don't get it.
Add in some nice variety. Give me holes that make you think, not just cookie cutter holes thrown into available land space to make a buck.
I also think customer service helps. Nice smiling faces. I remember playing a course for the first time that I've yet to go back to it (distance from home), but one of the things that distinguished it to me was the starter on the first hole. He asked if we'd played there before, and upon learning that we hadn't, gave us the "lowdown" on the first 4-6 holes.
I work on the maintenance staff of a, for our area, highend golf course, so I tend to be a bit spoiled, but I also look at things alittle different than the average golfer. I know the approximate financial situation of a lot of the courses I play at in the area, and I adjust my "critique" of them accordingly. If I play at a place where i know the superintendent isn't getting much funding for maintenance, yet he's got the greens rolling great, debris cleared, and the grass mowed, I give him a resounding thumbs up.