3e was a massive overhaul of the AD&D system. Very, very few mechanics managed to survive the transition and virtually none managed untouched. Going from 3e to 4e, most of the base mechanics are exactly the same. Stat meanings, D20 roll high, etc, etc. There are some obvious differences, of course - healing being a big example, but, even there, that's different from 3e to 2e. In 2e, you got Cure Light Wounds as a 1st level spell (1d8 HP) and Cure Serious at 4th. In 3e, you could convert all cleric spells to healing and it scaled by the level of the caster (with limits). Never mind the crafting rules changes.
IOW, play for the 3e character is almost the same between 3e and 4e. Mechanically, there's very few changes. Are they different? Sure. But, more different than the differences between 2e and 3e? Really?
I have to say you've made some really good points in these posts. Previously, whenever I've seen the 4E-is-the-most-different-edition claims I've given them a pass, without putting too much thought into it, since it seemed at least a reasonable claim. But having though about it now, reading your arguments, I think you've absolutey right.
And the funny thing is, I surely would have realized it had I just thought about it. I can remember the first time I played 3E. I had been a longtime player of AD&D, but then didn't play anything for about a year. Then I rejoined my old group who had started playing 3E. There was a lot to learn.
We were starting at second level. I wanted to play a fighter/thief, so I figured I'd be a half-elf.
What do you mean "you can be a human fighter/thief"?
What do you mean "which class was I at first level"? What the heck is a skill rank and why do I have so many of them? What in the world is "flanking" and why is it so important to me?
Now, ultimately it
made sense (ascending AC, the d20 mechanic, easy-to-understand multiclassing rules), but that didn't make them any less different. It took me a number of sessions to get everything down, especially in combat.
On the other hand, my wife's first game was 3.5. When we started playing 4E, I put together a brief summary of the changes that she needed to know, rather than her reading the whole book (which she would not have enjoyed). It took about 5 minutes to explain everything.
Starting as a 2e player, the first 3e book I owned (because it was a gift) was the Monster Manual. I didn't even see a PHB or DMG for months. I understood what AC, attack bonus, skills, and all that were intuitively. I also recall later playing the 2e/3e hybrid elements in BGII, which made perfect sense to me.
Weren't you at least curious as to why the more challenging monsters had
higher ACs? Or why a skill had just a bonus next to it instead of some number you weer supposed to roll under?
And as I said above, something can
make sense, even if it's very different from what you're used to.
As to the 3e-4e comparison, I do think comprehension of character abilities is easy enough, but I don't think that means that the games are fundamentally similar. They may both have an attack bonus, but how you get that bonus and what you do with it are both rather different.
You add your bonus (primarily gained through your level, your Strength bonus, and your magic weapon) it to your d20 roll and compare it to the target's AC to see if you hit. As opposed to having to compare it to your THACO to determine what AC you hit.
Ultimately I think the biggest similarity between 2E and 3E is the mechanics of spellcasting. But that's not enough, by itself (especially since it also changed a little), to cover the fact that almost everything else changed substantially.