I think the movie was slightly overhyped (2001, it ain't), but it's an excellent movie, with an incredibly rare combination of accurate hard science and touching character stories—something that I haven't seen since Contact.
The entire concept of relativistic travel still ties my brain in knots, and it's been a while since I took that college course on the metaphysics of time travel. But as best as I can tell, it all makes perfect sense, and is entirely self-consistent. Even once all the known rules go out the window after Coop crosses the event horizon, it's all completely consistent. A few of my friends don't accept the idea of the effect happening before the cause, but in metaphysics that's actually a reasonable concept.
I keep kicking myself for not figuring out the origin of Murph's "ghost," but I kept thinking it was the aliens (or whatever) who created the wormhole, and by the time the Endurance launched, I'd pretty much forgotten about it and was focusing on the rest of the action. The writers took such effort to stick to known laws of physics, that the idea of traveling back in time never once occurred to me. But by the time he started falling through the tesseract and slowed down a bit, I immediately recognized the back of a bookshelf and put the pieces together.
The only part I really don't get is the "water" planet closest to the black hole. If it was that close to experience such extreme time dilation, why is it intact? The black hole is pulling the oceans into such enormous tides (they didn't state that explicitly, but that seemed to be the intention... it wasn't really a "wave" but actually the twice-daily tide) but wouldn't it pull the planetary crust too?
Great acting all around, which isn't too surprising given the caliber of the cast, but especially from the girl who played the young Murph. I was expecting Coop's trip to take a lot longer than he intended all along, but it was still heartbreaking when he finally got back to see her.
If you haven't seen it yet, go see it in IMAX if you can. Spectacular visuals. My only complaint was the sound editing—there were several points in the action where I just couldn't hear what was being said, and that took me out of the movie rather than sucked me in more. Apparently it seems like that was a conscious decision to make the action more realistic, but I don't think it was a great choice. Not a deal breaker by any means, though.