I saw the Thirteenth Floor recently and thought it was pretty good. It got 27% rotten on Rottentomatoes, but two good friends recommended it to me, so I thought I'd go with their opinion over the critics. I'm glad I did. It's a good sci-fi flick. I actually think the story is strong enough to be made into a 10 episode mini-series or TV show. I'd definitely give that show a try.
It kinda got swept under the rug by the popularity of the Matrix (they both came out in 1999), and that's unfortunate. Obviously it has its flaws, but if you're into sci-fi, I think you'll like this movie.
I'd also avoid the trailer as it reveals too much of the story.