1E was about fleshing out the game.
2E was about streamlining and cleaning up 1E.
3E was about creating a consistent, unified, versatile ruleset.
4E was about making the system work smoothly in actual play.
I think this is by far the best answer so far, as it addresses the question from the perspective of the designers as opposed to the perspective of the various players - which will differ from table to table depending on how they played the game.
We can say something about what the designers were trying to achieve. We can't really say anything about how the rules were used by the players except to offer opinions about how we personally perceived or use them.
So any way, my take is probably no more than a restatement of what Dausuul said using different words but:
1) 1E was about exploration
2) 2E was about clarity
3) 3E was about consistancy
4) 4E was about balance
I would say that if you ranked these four attributes in terms of there importance to you in a rules set, it would reflect fairly well how well you responded to (or still respond) to the rules set.
If you like exploration, but care nothing about clarity, consistancy, or balance (and in fact perhaps consider clarity or balance to be anthetical to the best sort of play), then you probably fondly remember or still play 1e. On the other hand, if you care about clarity, consistancy, and especially balance, but don't care that much about exploration, then you probably love 4e and despise 1e.
I should note that I'm here using 'exploration' in a rather special sense, because I suspect that the previous sentence will spark an edition war if I don't clarify. By 'exploration' I don't mean the process of characters moving from a place to some new place ('adventuring'), but rather discovering new rules, new ways to interact with the world, and new elements of the world you didn't previously know existed. Clearly, if the rules are clear, consistant, and comprehensive, then you aren't as a player in the position of discovering those rules or new aspects of the game. In 1st edition, for example, you might learn that you can research spells or create magic items and do so not knowing at first exactly how it is done. By 3rd edition, this is no longer the case. You begin the game with this vista clearly in view. Hense, the experience of 'exploration' is very different between the two editions, and you can see why the 1e idea of exploration might be despised by some people and loved by others (even with both wanted 'adventure').
For my part, I rank the attributes consistant, exploration, balance, and clarity. With consistant being a short gap ahead of exploration and then a longer gap to the other two. I don't mind my rules being esoteric - indeed to a certain extent prefer it - because I've got a good memory and evocative and enabling is more important to me than simple. I want part of the game to be hidden from view so that you are encouraged to focus on world mastery and not system mastery. Balance is important only when the lack of it threatens to stop play, but consistancy and its partner comprehensiveness is very welcome for me as a DM because it gives me the tools to quickly judge any situation that comes up without stopping play to much.
