Roger Cruz, the usual artist of the series, takes a break to allow Eric Nguyen to illustrate this issue. For its Marvel character guest star, we get Man-Thing which, if I remember correctly, is Marvel's answer to DC/Vertigo's popular Swamp Thing. Unlike with the latter, I don't know a damn thing about Man-Thing so I can only discuss his participation here in the plot which is pretty marvelous. What was so gripping about this issue, aside from Nguyen's visual presentations, is the substantial plot that calls back what we have previously witnessed in the earlier issues regarding Bobby Drake and Jean Grey.
From what I can understand, Man-Thing has the ability to travel through dimensions. Is this canon? Maybe. I don't have the energy to research more of this character but for the sake of this story let's just consider that ability of his as gospel-truth. While in a mission, the X-Men encounter Man-Thing and they were transported into different timelines of human history in one blink of existence at a time. There were warriors on winged horses, Nazis on ships, etc. For a time the five of them managed to fight theit way through, that was until present and future started blending together and the team lost Bobby and Jean in the midst of the commotion. And if they don't find them before dimensions start closing up, they might lose them forever.
The real draw of this issue has to be the climactic revelations concerning the possible grim futures awaiting Jean and Bobby; worlds in which Jean becomes the Dark Phoenix as she slays everybody in her wake. Meanwhile, Bobby becomes a cruel Frost Giant and battles the Mighty Thor. The present young versions of these two somehow united with these grim future manifestations and the rest of the heroes have to find a way to pull them out while not freaking out as they watch their friends literally becomes nightmarish monsters. Fortunately enough, they were successful in saving both of them but Bobby and Jean also remembered what happened and are now going to carry those revelations from now on. It's up to them to decide if those futures will come true. After all, their choices will determine who they will become someday. They should have another follow-up to these character arcs later on because it's been enticing to read so far.
This is the darkest that Jeff Parker's series could get, I believe and it was a nice balance to all the fluff and goodness of the earlier issues and overall tonality. I certainly hope we'd start getting more mature issues like this one as we go on with the rest of the roster.