I thought it was quite good. If you basically like Harry Potter but find it infuriating how often the protagonists problems could have been solved in five minutes if they would have just told the adults... then HPMOR might interest you. Now, it's a didactic book, it's rather long, and you may or may not agree with the author's worldview, so whether you'll really enjoy it I can't say. But it's very well-written and in some ways tells a more "believable" Harry Potter story than the originals.
I feel like basically the only way in which the original Harry Potter story is more believable is that in the original story, almost everyone is impressively thoughtless
Well, in HPMOR, Harry discovers at the end he would have solved a quite major problem very early on if he had bothered to inform Dumbledore of some extremely important facts regarding Professor Quirrel.
