Generally very good, but I had mixed feelings towards it.
On the one hand, the cast is brilliant (although Bales accent was laughable, at least at first and Johansen's wasn't much better), it's well made and the script was generally good. The way it's presented (multiple layers, different time periods, different perspectives) was original for a major Hollywood movie and helped maintain interest. It's not the shortest of movies but I didn't find it dragged at all.
However, I thought it got rather silly and the climax (once you had been given certain information) wasn't that surprising. Indeed, many of the latter "twists" are far less clever than the film seems to think they are and are in fact bloody obvious (yet the film when it reveals them still thinks it's performing some kind of trick).
Perhaps I was merely unfortunate that my towering intellect surmised what was going on too early
but given that the person I saw it with had the same problem I doubt that.
Despite this, I would definitely recommend people see it, it's enjoyable and superior to most movies I've seen lately.