I suppose that Whedon's goal was to write a moving, tragic close to his run. Kitty appears to be gone for good, Colossus is sad and also gets a great angry moment, and it was e/affective in that way. There's a lyrical quality to the art, especially in these final pages. And, at least on the first read-through, it works.
And then you reach the end and realize that it barely holds together. Virtually everything else ranges from mildly to massively disappointing. We don't know how it is that the bullet Kitty's in is magic and disrupts her power (it just is; it just does); we still aren't totally clear on how the prophecy that Colossus would destroy Breakworld was planted; we don't know what happened to the Cure that Beast had, we don't know whether Cassandra Nova actually managed to implant herself in Armor in the previous arc; we don't know what's going to happen to Danger. (I could also list flaws in the storytelling as it pertains to this issue alone. I'll let Omar Karindu do that instead.)
These aren't inconsequential details. Each arc left us with questions, and what passes for closure in this final issue is incredibly wanting. Unless I missed something, we don't even know what the status of the Breakworld is after Colossus kills the rebel leader and Wolverine slices the arm off of the big angry dude. (I'd go back and check his name, but honestly... I just don't care.) Geoff Klock notes in his audio-review that it isn't enough to say that he's given subsequent writers options to play with. This has been a self-contained vanity project from the start (that Cyclops' blasts return inexplicably at the end of this issue would seem to indicate that Whedon knows that he has to put some things back in the sandbox) and it's very nearly unforgivable that he can't follow-through on what he started.
I imagine that I'll keep a certain fondness for this run. The pacing was a mess - like Battlestar Galactica, it's better consumed all at once so that you aren't conscious of how little content there is to each individual episode - and Whedon either forgets or inadequately explains a dozen or so plot-points from throughout the series, (Thanks to skullfire for this list!) but Whedon has made his name on his character work, not his plots. I suppose I could resent him for doing such a great job with Kitty only to kill her off (well, not really, but you know...), but he also gave me a reason to like Cyclops, made Emma sympathetic, and tried to make Colossus likable too.
So is the whole project a failure, in the end? I think I'd have to qualify my answer: a "yes" with a "but".