It comes directly in the wake of X-Men #66, following up several plotlines left dangling by the cancellation - Xavier's reintroduction, Magneto's aliveness status, the continued use of the plane liberated from the Sentinels, and Bobby's crush on Lorna. One unusual mis-step is the adoption of "Havok" as a codename by Alex, which he just sort of automatically does, despite it being only having been used by Larry Trask for him so far (although Lorna does point out its origin, at least). More of a big deal is made of Lorna not yet having a name: she plays with "Magnetrix", but eventually decides against it.
It makes more meat out of Zelda and Vera. They'd been unceremoniously forgotten about since their last appearance in #47, and Bobby here ends up on Zelda's doorstep having got rejected by Lorna. Zelda, to say the least, is unimpressed at his sudden reappearance into her life, especially once he explains why.
So I can't fault it's attention to detail, at least. But is it an artistically worthwhile thing to do, to go back and insert stories between 1970 and 1975 in a pastiche of the style? My colleague SpaceSquid thinks not, considering the overall endeavour to be hamstrung by its own po-facedness and decrying it as "guff". I'm less sure. I don't give a fig that the science is laughable, the timelines don't make sense and there's no appreciation of distance. I mean, this is superhero comics. It's not like a sense of place was something that X-Men ever had in this era. So I definitely think it's intentionally imitating hypothetical 1970s X-Men. But then with the Zelda/Iceman story, it's bringing emotional reality to a situation that frankly didn't deserve it. Bobby didn't abandon Zelda, the writers did, and fixing this up by having a storyline where out-of-world ball-dropping results in in-world abandonment points that out almost cruelly, while similar bizarreness in the work itself is left unchallenged.
Ultimately, I can't think why you'd want to read it if you weren't an X-Men obsessive who'd just read the first sixty-six issues. Byrne seems to realise that people are unlikely to be that familiar with the material - hence the epic flashbacks that reviewers complain about - but having answered the question: "what is going on?" it doesn't deliver an answer to "why should we care?"
It's got nothing new to say, and we know how it's going to end ("Good news, everyone! You're delivering a package, to Krakoa, the living island!"). And, as we'll find out, it directly contradicts the interstitial material that does exist. So to the general audience it has failed where First Class will later succeed.