I've been looking forward to this movie for a long time, and it absolutely lives up to the hype. I'm not 100 percent sure I'd label it Nolan's best work yet, but it's absolutely his most ambitious, and for a movie with such an incredible far-reaching aim he manages to deliver with really good focus.
Hard to talk too much about it without giving anything away, but it's absolutely brilliant. Not flawless, of course--I'm sure people will be able to find some small faults with character depth, for instance, although I think he greatly improved on this area from Inception, where that was one of the main criticisms. There are also some moments that seem a bit farfetched, but we're also dealing with concepts where we only have a very limited knowledge. There are also a few instances of corny dialogue, but for the most part I thought the script was well done.
Strong performance form Matthew McConaughey, who really is the vehicle that makes this movie work. Strong supporting performances as well, especially from David Gyasi and some others.
Overall, you will absolutely not regret it if you see it in the theater. Hell of an experience. Check it out.
Edit: If I have to give it a number rating I'll give it a 9 or 9.5/10.