Blizzard slaughtered replayability in Diablo 3 by making so that there is absolutely no point in replaying the same class again. Your max level Barbarian is, for example, every barbarian. Rather, it can be with just a few clicks.
In Diablo 2, your barbarian was THAT barbarian. You could start a new one and make a totally different kind and experience. You had to think your choices through as well so as not to make too many mistakes, which also made you extra attached to the character and the effort you put into it.
I stand by my opinion that the casualization choices they've made have killed off what once was Diablo. They have essentially put training wheels on a genre which made its name by not having training wheels.
They've instead of modernizing the genre simply switched it out to safe and bland. I'm sorry. I can't see Diablo 3 as more than a graphically really nice, and gameplay-wise adequate (it's too easy for far too long for example), hack'n'slash with as much depth or even less as the PS2 title Dark Alliance. It's just a shade of what Diablo 2 was.
What are they thinking? And starting a real money auction house? That would only make sense if you could in fact make tons of different character builds and have reason to sell and buy and experiment with different setups. It would have made sense in Diablo 2. But here? You've got your max level character and there is really not that many different sets of items suitable for it. You're a barbarian? Alright, have a mix of vitality and/or strength.
Unless... they're planning a World of Warcraft and release many expansions that simply increase the level cap ever so slightly, just to inject new items into the game and have people buy/sell those in the auction house so Blizzard'll get their cut. That's the only realistic plan I can them having, unless they've simply just f-cked up.
- After having had a day to reflect, I update:
Of course; that's the point of Diablo 3 having the "one character is all builds". You only need a few clicks to change character build (something that took creating a new character and going down a new path in previous Diablo games), and can much faster purchase new fitting items off of the real money auction house, where a cut goes to Blizzard.
And, of course, the various builds must be designed in a way that you'll need the correct gear for them and you can't just go with a few different items. That would make Blizzard's strategy perfectly clear anyway, and they're not ones to not think things through.
Blizzard then doesn't have to wait for you to build a new unique character up to buy those items - they can just sell you your needed gear (which, essentially, they've disguised as a "player driven" auction house) whenever you need it. It's designed to make you want to buy the things from Blizzard instead of grinding for them yourself. Yes, there is an in-game currency auction house, but most people will obviously want to sell things for real money when the real money auction house goes live (in a few days).
And it's all for the "endgame", mind you. Of course. Because that's Blizzard. Their RPGs can't seem to follow anything but the "oh just you wait, it gets fun in the end (after some 20-30 hours of grinding)" mentality.
Diablo 3 is through-and-through designed for being a game experience fed by microtransactions; the concepts are two halves of the game - the auction house was not designed to be "an addition".
- So a TL;DR.
Question: Why does Blizzard slaughter replayability in Diablo 3 by making classes be able to change build at any time?
Answer: Because they want to sell you items through microtransactions with as little delay as possible, disguised as a "player driven" auction house. Because of this disguise they could charge a premium fee for access to the game, and, because of this same disguise, the pricing of the sold items can theoretically be ridiculously high and the players, not Blizzard, will get the blame for being greedy.
It's fucking genius.
Note that I'm not trashing Blizzard. They know their business. Am I disappointed with Diablo 3 as an old Diablo 1 & 2 fan? Oh, yes. But I've got myself covered there.