I just watched The Machinist. Interesting movie. The most striking thing, almost an extra character in the movie, is Christian Bale's emacited body. He starved himself for this role, achieving an incredible, disturbing skeleton state that had me distracted for the first ten minutes.
The movie is ok. I had high expectations - Christian Bale is typically a guarantee of a good movie. This has a nice creepy, disturbing feel all the way through. The story line is not terrible, but not great. The twist is decent.
If you liked Fight Club, you may like this one, although Fight Club is a much better movie.
I was going to use a number based rating system, but these categories makes more sense to me: Avoid, Watch if you've got nothing else to do, Watch if it comes your way, Go watch it, Go out of your way to watch it, and Go right now, track it down, and watch it.
For The Machinist, I'd say Watch if it comes your way.