People, I started out in AD&D2e, went to other systems and didn't really look back. But I've tried games in all the revisions, though, even if they were shorter story arcs or one-shots.
And in my opinion, you are comparing apples to oranges. Sorry, there was no better way to put it. And FYI, peaches are better
Now, seriously, I can think of multiple games that are closer to one edition of D&D than another edition. Switching from 3.X edition to a lifepath-based system would be much more painless then to 4th edition. Maybe the designers actually wanted to do something closer to lifepath systems? It's a good design choice, by the way, and part of the reasons I voted for 3.5-3.75. Or going from 1st edition to a random rules-light fantasy game, and so on. Bottomline, they are different games
to me, not just different editions of the same game.
I mean, they've got almost all design choices different between them. The fact that the attributes are named the same way, you've got alignments, saves and hit points and you roll a d20 are pretty much all the common points remaining from 1st to 4th edition. Yeah, I'm sure I might be missing something, but let's look at the things that really change the gameplay, ok?
Note that I'm really doing that analysis for fun. Also, I'm as impartial as you can get, not having strong preferences toward neither edition. I can paly lots of different games after all
Relation between mechanics and fluff.
1st edition mechanics, from what I see in free games and from what old-timers on RPG.net told, were meant to be in the background for most of the time, but you had to rely on the GM a lot. 2nd edition mechanics gave you some degree of guarantee the GM is not going to blast your character with fiat, more choices, and more "pollitically correct mechanics", without assassins as a core class. 3rd edition, you can play all the time mechanically, but mechanics are often not into the background, and you can fail to make the right mechanical choices which means the character is a mechanical failure as you progress in levels. And in 4th edition, mechanics pretty much determine gameplay.
All in all, you get most freedom in your concepts in 3.X, by combining different classes. Still, that's not a major advantage, as with custom classes, you can get the same in any edition.
Balance and fairness issues.
You were not supposed to get balanced opponents in 1st Edition. If you had a bad random encounter, you run or died, or ran and died. Same thing in 2nd edition, but with GMs advised to roughly balance it out. In 3rd edition, if you get in a fight, it's likely to be a winnable one, that's what CRs are for and even more likely in 4th edition. On the other hand, getting a "better" character was assumed to be part of the fun in earlier editions. You were supposed to compensate by thinking quickly and keeping to your niche. In 3.X, they at least tried to do them more equal. And in 4e, you have mandatory equal characters for the same roles - unless you buy only this upcoming book, and that one, too...
Random character creation
Randomness was supposed to determine what you played back in 1st edition, but you were able to make a new character in minutes. Every subsequent edition took you further away from this. Character creation can take hours in 2e, days in 3rd Edition or 4th edition. It's actually a mini-game within the game. However, in 3.X, you get punished for making the wrong choices. In 4e, bad choices are reversible. On the other hand, in 1st edition you're pretty much stuck with the concept you picked, or rolled for. in 3.X, multiclassing is way easier. And in 4e, you are going to play what you began with.
The power of PCs.
You get more and more out of being PC in any edition. Compare the "3d6, roll in order" to 3.X point-buy and lesser classes for NPCs, and even there, a wizard is pretty fragile. Not anymore in 4e, the developers don't want someone writing them frustrated emails because their wizard who didn't get combat training gets hacked to pieces in the first round of a combat with a combat specialist. Can't allow that to happen anymore
OPTIONAL RULES is key here. In 3rd edition and 4th there is little flexibility. An example could you take out Feats in 3rd or all those quirky class powers in 4th? At least in earlier editions like 2nd you could simple say non-weapon proficiencies are not being used, no subclasses or so forth and the system easily accomodates that. Where is that option in the post-2nd Edition? I would love to have seen feats, odd class powers like healing and how magic is used optional and allowing the DM to opt out.
And you failed to note the playtest issue there is a reason 2nd edition stood for two decades it was lilely the only game playtested by fans, inputing ideas from fans and had fans saying what they wanted in the game during the key part of the development process. And that also eliminated most of the things they might have had to revise such as the 3.0 to 3.5 RIPOFF. And they seem to have done the same thing again with 4th edition.
Just to point out, most GMs in 3rd/3.5/Pathfinder Edition I know consider anything but the core book "optional rules", so you'd have to check it with them before creating an "expansion" character
. And even core feats and spells might get banned, if they don't suit the campaign they intend to run, or a setting. I expect them to be doing the same with 4th Edition now, whether it says every book is core or not, and I think it's fine.