Old Gumphrey said:
When exactly did previous editions serve as a simple way for new players to learn the game?
The first "D&D" boxed sets were an excellent entry point. In the early 1980's, TSR sold more than a million of those sets in one year. They had wide enough distribution that they got D&D into the hands of a significant portion of the people likely to find a hobby in the game. At no point since that time has the D&D publisher achieved that level of success.
And, not coincidentally, D&D core book sales have never matched the 3-5 year follow on period after those halcyon days in the early '80s. I feel those two facts are directly connected.
However, the leap from those boxed sets to the core books was tremendous. 1E suffered from a lack of a coherent design strategy. 2E suffered from a desire to take control of the game away from the players and make it reside with TSR for the purpose of building campaign settings and thus novels and software. 3E "suffers" (if you can call it that) from giving players so many tools they are overwhelmed by their options.
3E is, at heart, a very simple game. The complexity of the game comes from the number of choices that you >could< make. One of the things that most people don't see about 3E is that at any given time, the number of choices you >can< make is very, very limited. 2E trained a whole generation of gamers to be ultra careful about what choices you make early in a character's lifecycle, because those choices will be determinant throughout the whole of that characters' time in the game. As a result, 2E players often freeze when confronted with their options at character creation - afraid that a misstep will cost them dearly six months later when they realize that they've trapped their PC into a dead end with no hope of escape (something that happened often with 2E).
3E also has a strong emphasis on the idea that there should be a rule for each situation, not a judgement call. We found that by and large most DMs preferred to have a rule rather than be asked to make an arbitrary decision. We found that players overwhelmingly preferred to have a rule. In my personal opinion, these two factors are related. I think that most DMs just don't do a good job making arbitrary decisions, and they know it. And most players react badly when an arbitrary decision goes against them, and they dislike the experience intensely. In my opinion, the uber-DM who flawlessly runs a game by "winging it" is, was, and will be a myth. Observation (of hundreds of DMs) leads me to conclude that often when a DM is "winging it" the satisfaction of the players goes down.
D&D is a roleplaying >game<. It's not improvisational theater. Games have rules, and they are supposed to be played by those rules. I think that part of the perceived "complexity" of 3E comes from people who would prefer free-form roleplaying, rather than a "game" experience. Confronted with rules for the game, these people withdraw, citing "complexity" when their real complaint is against "rules at all".
The other thing that 3E does pretty convincingly is define the game in terms of "classic heroic adventure". D&D is the game where you fight monsters, take their treasure, and power up. If you are interested in other kinds of roleplaying, like courtly intrique, economic manipulation, etc. D&D 3E is not a good fit for your interests. I think this is an improvement, as players now know clearly what they're supposed to be doing in the game, and if they want to do something else, they need to get consensus from the other players and the DM, rather than just assuming that they will get what they're looking for automatically.
The downside is that "classic heroic adventure" is pretty much combat-centric. As a result, the game is combat-centric, and combat rules are esoteric until you've used them enough to gain mastery. 3E does a terrible job (as does 3.5E) of bringing a new player along gently. The combat system is presented as "integrated", and there's no provision made for starting with simple combat and moving to more complex combat as people become familiar with the rules. I think this could be ameliorated via a short "combat for beginners" section that did away with AoO, grappling, charges, reach and threat zones, and presented all actions in combat as full-round actions. When I teach D20, that's how I teach new players, leaving the more advanced "tactical" aspects of combat for after they understand how to cast a spell, swing a sword, shoot an arrow and run away.