This story has in many ways set the tone for all comics in this franchise right up to today. It was at the time just one link in a chain of major storylines dreamed up by Clairmont, but is now seen as a major point in not only X-Men history, but mainstream comics on the whole. For example, let's look at what pieces are present here:
1) As stated, Wolverine gets plenty of face time, and his multiple homicides are ignored.
2) Cyclops is shown as a competent leader, powerful fighter, and compassionate person, but is not written as doing anything terribly vital.
3) Jean taps into Phoenix powers, dies. Hints at drama with the previous two.
4) There's an emphasis on the growing divide between the Professor and the team, which has only recently become an issue again. Then again, I imagine since he's dead now, it's a bit moot.
5) Lots of people get involved in stories. This is to me the hallmark of X-Men storylines, with heroes and villains from all over showing up, often in unexpected roles.
There are some clear signs of DPS, great as it is, actually not being as good as it could have been. For one, since trade paperbacks were not collected at the time, the recap dialogue is ever-present, since a reader may have missed the last issue (thank Buddha for the modern recap first page). The other is that some plot points reek of editorial mandate, "Quick, we need a character to reach out to that new demographic! Make a disco character!" Oh, the immense fail that is Dazzler, whose name was originally supposed to be "The Disco Dazzler."
Nonetheless, it's a classic story that's earned it place. No wonder this is the fourth time the story's been printed; once originally, once in X-Men Classics monthly, and two printings (at least) in trade. It's kind of a big deal.