I'm more of a gamer than a D&D'er. In fact, only after playing lots of other games do you appreciate the flaws that still exist in D&D and really see the need for change. We played OD&D and AD&D (never played any of the iterations of Basic, never knew anyone who played Basic - we went straight from OD&D to AD&D and never looked back) for many years, but most of my AD&D play was under a GM who was 'story first, rules second'. If there was a rule that got in the way of replicating how a scene played out in a book, then the rule died or was replaced. He had a huge wall-map of the subcontinent we adventured in, and books of city maps and customs and NPCs and we spent years exploring it. 1E's clunky spell system was one of the first things to die; playing in straight-up 1E games was like having teeth pulled after we were set free from the strictures of it. He used a couple of third-party things and some house rules. Racial limits died next, then the silly notion that you got XP for treasure. But if anyone asked us, we'd have said we were playing D&D.
Another group, we played tons of Traveller, Space Opera, and other systems.
Near the end of 1E, we'd all but abandoned D&D.
Over the years, we moved to less-restrictive and dogmatic systems. The Basic Roleplaying Engine was our first real 'generic' system; RuneQuest, Call of Cthulhu, ElfQuest, and Superworld was what we used mostly. The BRP engine was our 3E for a decade or more; simple, adaptable, expandable, used one single mechanic for many many things - to this day we are still totally baffled as to how Chaosium is not at least the second biggest RPG manufacturer in the world.
And Champions. God, we loved Champions. And Star Wars and Marvel Super heroes, and a number of other games. Two groups I played with loved Rolemaster and I liked it fairly well, but never could get my main groups to try it. One group loved GURPS but I never could get into it all that much, save by ignoring 90% of the combat rules. I ran it once and it was OK, but I had no real burning desire to do it again. I've done a few sessions of it since then, but we were far more concerned with characterization and worldbuilding in those sessions than with rules.
We still played 2E D&D but mainly as a change of pace.
We've never ever used the Great Wheel. Only one guy ever used the Forgotten Realms. We never played in Greyhawk. Never used Sigil or PLanescape or Spelljammer - basically, all the stuff 2E did, we'd already been doing for 10 years in other game systems. 2E was too little, too late.
Vampire was a massive breath of fresh air. We played the hell out of that game. We never went in for Werewolf, Mage or the rest, but we stuck with 1E Vampire, only gradually moving to 2E or Revised or whatever the next thing was.
3E changed all of that. It had enough changes that D&D suddenly became the expandable, adaptable game we wanted and finally there was a group of designers that saw this as well and showed us how you could do horror and superheroes and space and westerns and other stuff all with D&D. We've seldom played anything else for the past seven years or so -- and to us, 'd20' and 'D&D' are the exact same thing. Same basic rules set, same game. Simple as that. No arguement from anyone. Mutants and Masterminds and True20 are 'D&D/d20' to us. So is Conan, or Blue Rose, or Midnight, or Arcana Unearthed, or Iron Heroes.
I've run Savage Worlds, and liked it quite well. If 4E turns out not to be what we want, we'll probably either move to that, or move to some variant of Arcana Evolved or True20.
We've played a lot of systems. Much like I think that a substancial amount of fiction reading is a requirement for truly enjoying gaming, I think that playing other games is also a requirement for truly enjoying gaming as a hobby. Staying with one thing is like eating only pizza breakfast, lunch, and dinner. It may be good for a time and you may enjoy it, but eventually you'll get scurvy and die from it.