There. I said it.
Now, I better be careful here. I'm not saying that it's dreadful, you understand. It's just it simply cannot withstand the heaps of praise placed upon it.
Jean, who has been messed with by the Hellfire Club, manifests as the Dark Phoenix in Central Park, and flips out. Scattering the X-Men, she then flies into space, and starts eating tasty suns. In particular, she eats D'Bari, destroying five billion souls. At this the Shi'ar, allied with the Kree and Skrulls, decide that the Phoenix must be stopped. She then returns to Earth, to her childhood home in Annandale-on-Hudson (and we meet again her parents, this time adding her sister Sarah - who is a mother herself), where she is confronted by the X-Men, in a last desperate stand. Briefly retaining control, she begs Wolverine to kill her, but then recedes into insanity again. After a mental battle with Professor Xavier, she is able to retain control, taking again the name Marvel Girl.
At that point the Shi'ar turn up. They're gonna kill her (how do they plan to do this exactly is unclear), but instead they are challenged to a duel by the X-Men. We then get a dozen pages of X-Men fighting the Imperial Guard. Dark Phoenix then manifests again, begs to be killed by Colossus (he's reluctant to, saying he's never killed before, the liar). Ultimately Jean triggers a Kree deathtrap left here on the Moon (did I mention this was all on the moon?), and passes away.
So, first problem: lots of this plot relies on our characters being either plain idiotic, or making unforced poor decisions. Cyclops not picking up the phone, Xavier leaving for the Shi'ar before he's certain what's going on with Phoenix, Jean not telling anyone about the timeslips until too late, and then the decision to infiltrate the Hellfire Club, thus handing them Jean on a plate. Secondly: the theme of "absolute power corrupts absolutely" is paper thin here. There's no consideration of the mechanics of how that happens in actual human psychology. It's just treated as a sort of biological law, like it's gravity or something. Thirdly: well done on killing off a crazy, not particularly well-characterised woman, who can't deal with advanced mental powers and was attracted to the idea of living more simply in the 1780s. Way to go there, supposedly progressive comic book title.
Particularly since she was presumed dead, Scott has sensed there is something wrong with Jean, that is wasn't really her. That's a pretty good out, if they ever decide to bring her back.