It got much better probably through the 6th or 7th time I saw it, because with each viewing I was catching little nuances placed within the film (such as Leo's wedding band for instance). I think it has a lot of replay value overall because of the layers of the film which is required through the plot, thus it's a pretty fast paced film. I've actually found The Dark Knight to be a little lengthy the more I've watched it, particularly with the ferry scene at the end (which is necessary it just drags the film a bit long IMO).
Haven't felt that with Inception yet, only beef I had with it after multiple viewings is that they cut back to the falling van from the bridge a few too many times, as if to say to the audience, "remember why everything is going on in the other levels." I felt this could have been handled a bit better from the standpoint that it could have been shown maybe 3 times, once as it goes off, one in the middle and one right before the end....and hell for all I know it was 3 times that it was shown, but it felt like 5 or more.
To me it gets better and better. I don't think I will ever get tired of seeing this movie. I saw it twice the opening day and haven't stopped since. I always try to pick new small things with each viewing and I usually always find something new.