We see Jean failing to get Scott away from writing his report on Krakoa to discuss things, which makes her leaving him seem much less cruel. Bobby is a bit off as he gets super-annoyed with pretty much everyone. Bits are anachronistic - Banshee gets a name (Sean Cassidy) before it gets mentioned in the series proper. We get Peter's sister's name (Illyana, which, by the way, isn't an actual Russian name - more on that when she's introduced in the series) early, and find out that he draws, that Banshee plays piano and likes country and western (something established already in the pages of Captain America).
Wolverine (who admits to being a killer) hits on Jean, and Warren steps in to defend her honour, rather unnecessarily. Both Jean and Warren are leaving the team in part because of Wolverine (Jean because she's worried she's attracted to him, Warren because he thinks he's a dangerous lunatic). Alex and Lorna, who we'd never really seen as part of the team proper in the original run, don't think they're needed any more, and are going back to college...
As I say, it fleshes out a gap in #94. It's not exactly seamless, as it uses Claremont's later characterisation of these folks, rather than how they really were being written in 1975. Not vital, but nor is it claiming to be. In short: a nice little bunch of vignettes.
But, it's just a regular sized comic - the total page count of X-Men Classic #1 is reduced from Giant-Size. How did that happen? Well, the entire bit on Krakoa has been reduced to a two-page summary. Huh.