It's brillant up to episode 17, in which the Laura Palmer case is, well, "solved". Thereafter it's not as tightly constructed. There are some unnecessary storylines besides the main story. It could have been a bit shorter, down to maybe about 26 or 28 episodes instead of 30, but overall I like it as a whole. And it has a great ending.
Haven't seen the last episode again for now, but as I'm remembering it, it was a great way of ending Twin Peaks. Of course it would have gone on for another season, if it had still been successful, and the next season would have been centered around the White Lodge, at least so I think.
The first possible end could have been after # 17 with Lelands salvation, an optimistic ending with a slight pessimistic touch in the last shot of the owl and the woods.
Whereas # 30 ends in a very downbeat way, and that's for me a perfect end for the series, cause Cooper's "transformation" seems to me as a logical and fitting climax for the whole conception.
Of course, viewed as an end, and not only as another cliffhanger, it's an open end.
And there were not as much open questions and motifs as after # 17. But I never had expected that everything in the series would be explained, the openess was always part of the fun.
Viewed as an end, the explosion is also no cliffhanger, but stands for the death of several of the main characters, which is also very fitting.
The only real cliffhanger I'm remembering concerns Ben Horne.