In Diablo 2, there was relatively little emphasis on end-game. Actual end game was pretty difficult to even reach. Not very many people in D2's history ever actually made it to the level cap; it wasn't even necessary. You could beat Hell Baal without being level capped. Being level capped was only an actual goal for a very small percentage of players. There were no item drops that required the player be at level cap; sure, there were some that required high levels, but even once a player reached that high level required for the best gear, there was still room to grow beyond the highly random nature of gear drops. And yes, there were cool things (Uber things, even) for the highest level characters, but they did not come at the expense of the lower levels.
Throughout D2's lifetime, there were numerous tweaks and patches, as well as the major content upgrade that was Lord of Destruction. And all of these tweaks and patches introduced content that was relevant to any character in the game, not just to characters at level cap. Even the expansion introduced content that was applicable to all characters: a new Act accessible from any difficulty level, new character classes, a slew of new items and uniques, etc... There was no emphasis on the end game in these content upgrades. When charms were added, they were accessible to all characters. When runewords were added, they were available to all characters at all sorts of levels.
In Diablo 2, the journey was the whole point of the game.
By contrast, in Diablo 3, all the best gear requires you to be at level cap. To even get to the highest levels of the game, you have to be at level cap. That means that the character progression of leveling up is not the focus of the game; the focus is to get to level cap as quickly as possible and begin collecting the highest gear. All design decisions are centered around this idea. In a way, the true game only begins at L60; at that point, you finally have access to all the skills and runes, all the best gear, and so forth.
In Diablo 3, the destination is the whole point of the game.
This distinction is only further hardened by the things that people perceive to be improvements over D2. The skill system, for example. The skill system is designed so that you never have to re-roll a character. You can always change your skills, as easily as changing weapons in a shooter. There is no danger, as there was in D2, of ending up in the highest difficulty with an invalid character. This is seen as an improvement. However, this automatically makes the assumption that the time spent leveling an invalid character is wasted time. In a game that emphasizes the end-game, then this really would be wasted time. In Diablo 2, however, it was not. A great part of the longevity of the game was based around the idea that re-rolling a new character is not a bad thing. The whole closed-battle.net ladder system was founded upon this idea. Everyone in the new ladders re-rolled a new character. Characters weren't regarded as being as permanent as they are now.
Re-rolling to try a new build is only a waste of time if the end-game-centric design of the game makes it a waste of time. Perhaps this is a cultural shift among gamers, but if so it's a bad one, in my opinion. Why should the process of leveling up be considered time wasted? Shouldn't it be fun (or be made fun) in and of itself, rather than just as a hinderance to reaching the end game?
For this Diablo 2 player, at least, leveling up was never a waste of time. I ended up with a great many characters that were not viable in Hell difficulty. It didn't matter; I was perfectly willing to salvage their equipment and start a new character. This time, I would try something different, something new, to try to make it more viable.
When you take the joy out of the journey, when you push players toward the end game because the end game is all that matters, you put yourself into a difficult spot. People will consent to be rushed to end game, whereupon they will quickly run out of "content". In fact, it's this whole idea of "content" that drives this end-game-centric mentality. Content, by the Diablo 3/WoW measure, is stuff you do at the end game. But in Diablo 2, content was stuff that you did along the way.
End-game content and the mentality that drive it are fine in an MMO (although even there, the focus on end-game causes problems) but many people who loved Diablo 2 and were looking for improvements upon it may be less inclined to be accepting of the end-game focus in Diablo 3. They took away the ability to incrementally grow my character in ways that I direct, taking away the ability to incrementally upgrade my skills and stat point distribution, because the leveling process is just a "waste of time". They gave all level-capped characters access to all skills, again because leveling up is a "waste of time". The problem with this is that once the level cap is reached, there is no incentive to start over and try something new. Why should I start a new wizard, when I already have a wizard? That, right there, eliminates a huge part of the replayability.
Diablo 2 lasted over ten years, with relatively minimal money spent on tweaking it and updating it. Diablo 3, on the other hand, will require huge sums of money and time to expand and improve, because all improvements will need to be "end game content", with all that entails. There is no point in adding a whole bunch of early game or mid game content, because the player base will have already have been pushed to level their characters to cap, and leveling again is a "waste of time". I have leveled multiple sorceresses in Diablo 2, but I will only ever level one Wizard in D3.
I think this might be part of the reason you see far more complaints about the game in the General Discussion forum than in the Hardcore forum. The Hardcore guys, for the most part, "get it". For them, it's all about the journey. Their very survival depends upon them focusing on the here and now, rather than the ultimate goal of end-game. So perhaps it is merely a matter of gamer culture and perception. It's just a shame that Diablo 3's design philosophy encourages that end-game-centric perception.
Blizzard does seem to have learned a few lessons over the past decade; unfortunately, the lessons they chose to act upon were those taught them by World of Warcraft, and not by Diablo 2. And it is those lessons they chose to draw upon when they made Diablo 3. The result is a schizophrenic mess that tries to be both WoW and Diablo, and fails at either. That is why this Diablo 2 player is confused and angry.
Anyway, I guess it is for the best. D3 was starting to cut into my GC development time. However, a dismaying consequence of my time spent with D3 has been an urge to revisit the ARPG prototype of GC. To make things go boom, smash, explodinate. Ugh.