I guess I shouldn't be surprised this was a runaway success. It wouldn't be the first time Chris Claremont and John Byrne's X-Men connected with an audience.
The Fantastic Four discussion continued to pay dividends, as the class initially devoted their attention to the art and even the coloring and their impact on the storytelling. It helps that the creative team gives them plenty to work with--this is far and away the glossiest, most professionally polished book we've read yet.
John Byrne is at the absolute top of his game in these issues, and while everybody acknowledges that he helped make the X-Men a fan favorite, we never seem to discuss how or why. The class talked about the detail of his line drawings and the fully realized backgrounds as enhancing the clarity of their reading; they especially praised his ability to guide them in and out of Jean's timeslips through his layouts. Our supplemental reading from Richard Reynolds contributed an analysis of Byrne's manipulation of point of view to guide our attention and our identification with the characters, and the class added some great points about his representations of solo failure and team success in the book's group dynamics. All of this was enabled by the precise inking of Terry Austin, of course, just as Claremont's verbose scripts could only work with the pristine, compressed letters of Tom Orzechowski, and virtually every part of the creative team received our attention, all the way up to Jim Shooter's infamous editorial mandate. The class has honed its visual analysis and its awareness of the creative labor that goes into making comics, and X-Men provided plenty of opportunities to sharpen both.
And then there's the writing. In the first class discussion I couldn't restrain myself from mocking Chris Claremont's melodramatic scripting and his infamous verbal tics (My life. My choice), but these defensive jokes had no meaning for my students--this is the only Claremont they've read, and they liked what they saw. The melodrama was a selling point, as were the emotional, intensely self-conscious dialogue and narration.
One of the more notable features of the Dark Phoenix story, if only by its absence, is the almost total lack of scenes portraying mutants as a metaphor for real-world minorities, or the traditional integrationists vs. separatists plot that usually goes along with that. (To the extent that it fits that plot structure at all, the X-Men's mutant rivals in this story aren't the usual radical separatists but a group of shadowy power-brokers so ultraconservative they dress like the founding fathers.)
This works very much to its advantage. Metaphorical readings of the X-Men almost always fall apart on close examination, and they lead to shallow interpretations like this project, which confuses changing the X-Men's skin color with changing their race. David Brothers sums it up well in the comments: "They posit a surface-level thought experiment for something which requires more than a surface-level appraisal." This is true of most metaphoric readings of the X-Men, the affirmative as well as the critical, with the possible exception of that one primal metaphor that Claremont sketches out with such uncommon efficiency: "Kitty's at that... awkward age." Mutants have always mapped onto their (once-) adolescent readership better than they have to any real-world minority groups.
The Dark Phoenix story doesn't have room for minority metaphors because it's mostly concerned with a completely different (and potentially far more disturbing) set of metaphors as Jean pursues the ultimate in self-gratification, a genocidal and self-destructive path that Claremont would call "the quest for the cosmic orgasm." That led to a rich discussion of the story's sexual politics, although typically for most critical evaluations, I had to float it myself before the class felt ready to join in. The association of Jean's corruption with her sexual maturity and assertiveness is troubling, but it also rewarded close analysis and discussion, especially once we read Sean Howe's account of the creative struggles over the ending.
The Claremont/Byrne X-Men continued to demonstrate, a couple weeks ahead of schedule, that we've arrived at the point where we can discuss these comics using the tools of literary criticism. But now that no longer seems like a novelty, and the class is ready and willing to take up the challenge.