I think one of the things that makes the original work is how merciless it was. No tutorial or early game shit missions like newfaggotry, you will learn by getting slaughtered in eight-alien small scouts like the scrub you are, then thoroughly sodomized in Terror Missions. You either ragequit like a faggot when you get a squadwipe by Cyberdisc and Mind Rape, or you become a fan.
As I recently wrote in a different thread, I kinda disagree. NuXCOM devs came to the same conclusion you did, but what was really great about old X-COM was that it allowed you to play however YOU wanted.
Never want to lose a single soldier? No problem, save regularly and scumm to your heart's content.
Want to play ironman? Just make up your own houserule and do so.
Anything between those two poles was possible, the game didn't try to force you into a straitjacket.
Plenty such possibilities for houserules greatly increased replayability and thus longevity.
You were at liberty to do even inefficient things, like playing a no-plasma-weapons run (or even a conventional weapons only run), using no offensive psi, no flying armor, tackling difficult missions with a skyranger full of rookies,yadda yadda yadda.
Compare that to XCOM where not getting enough satellite coverage at exactly the right time could sink your game (at least it could in early vanilla).
It's systems are much tighter and allow for a lot less bullshitting around. And the game is off worse for it, especially when it comes to replayability.
Also, I feel like a huge boon of X-Com was the semi-realistic gameplay style, supported by it's excellend music and sound. Everything appeared to be perfectly balanced.
It's funny that XCOM, with much higher resolutions and realistically rendered graphics (though with a slightly cartoonish style of course) feels much more "gamey" than such an ancient game with pixel graphics.
I agree with most everything else you wrote though.
I loved Apoc, but I feel it's ultimately held back by it's not as appealing artstyle.