To me what I liked Decimation and the killing of many students in Xavier Institute is there were just more or less 23 students left that we could have followed for years. I was like oh 198 mutants? It was like exciting how many would survive in the coming years. Then outside of the mansion, those who weren't doing nothing at that time (Marrow, Stacy X) had some sort of a final chapter or a reason why they weren't gonna be used anytime soon like Jubilee.
I hated the Decimation because they made a definitive list of characters who were depowered without a story showing it happening to them (directly). Now over time they got away from that list, which was good, because there were a lot of minor characters whom I liked that were suddenly depowered and likely never to be seen again. For those who got that closing chapter like those you mentioned, it was good... but for others it was the same as killing characters off panel.
But of course Young X-Men, Second Coming, Five Lights, two schools came along and poof it became hard to keep track of every mutant under the X-Men wing. That's why I wanted the terrigen mist to wipeout like 75% of the mutant population. And I just can tell the newbies of Generation X would be doing nothing in the coming years, so I didn't bother to read it (and the artwork is terrible, though I like the covers). Then out of the new faces, no one really became popular except for X-23 for obvious reasons.
I agree about Generation X. The art is horrendous and the student cast is horrible. In fact, most students post-New-X-Men are horrible.
Now when it came to the students, I did like the whole Decimation/Childhood's End arc. I liked that the vast amount of students were chopped down to a manageable number which was then followed by a sense of survival of the fittest among them.
I hated that New X-Men was canceled at its height and that a lesser lineup of survivors was formed for the follow up Young X-Men... but it was still the same generation, so that was fine. And it kept the survival aspect by killing Wolf Cub in the first arc. It was after that when the Generation Hope students took center stage, and then Bendis' kids, the post Avengers vs X-Men kids, etc. I mean, I don't mind an additional student here and there... but whole groups/generations of them while the previous generation just floats around in the background? Lame.
The quality and development of the New X-Men (and other surviving students of that era) was phenomenal, and they were just hitting their prime. I don't know what goof at Marvel made the decision that they were no longer necessary, but they killed a generation of X-Characters who had the potential to be the next New Mutants (far surpassing Generation X... who is my favorite).
Just for fun... of those who came after New X-Men... these are the only characters I actually liked:
Generation Hope
Transonic
Kenji
Wolverine & the X-Men
Genesis
Broo
Kid Gladiator (kinda)
Bendis' Uncanny X-Men
Tempus
Triage
And the funny thing is that NONE of those characters are used anymore. But nonetheless, since the New X-Men generation, I've liked 7 out of around 25 new students.
Now of the New X-Men generation CURRENTLY ALIVE: Prodigy, Hellion, Elixer, Mercury, Surge, Rockslide, Gentle, Anole, Pixie, Mercury, X-23
So off the top of my head I like more New X-Men at the moment of the title's cancellation than of the 25 or more students since. And the reason is that there were less of them and they actually went through real character growth. There have been so many since then that they're just showing up and then disappearing when the next writer comes along and does a student book. It's annoying.