First of all, I'll be honest. I haven't played Diablo 3. I was hoping to get into it with Reaper of Souls, but from the feedback I'm getting, there seems to be no point in that. I have, however played Diablo 2, a massively popular mod of it called Median XL, torchlight and van helsing.
Whenever I see one of those threads as to 'why is Diablo 3 a bad game', I feel like posters make some good points, but they mainly focus on some specific things, and miss the overall picture. You see, the thing is, not everything is appealing to everybody. I think the challenge in making a good ARPG is to have all the features, so that at least some of the features will appeal to each player.
I'll briefly discuss these features with respect to Diablo 3 and why the Dev team really dropped the ball on most of them.
1) Online only. This is frankly a big deal for me. I don't have a good internet connection all the time. I don't want lags and disconnects. Especially in HC. Also, I don't see why I would want to be dependent on Blizzard's mercy as to whether I can play or not.. like if their servers are down or someone hacked my character or whatever.
2) No Modding. Related to the above point. Virtually all long lasting games have dedicated mod communities built around them. But guess what? You can't mod Diablo 3. No prizes for guessing why- it's because they obviously fear someone creating a mod that is much better than their actual game..
3) Limited character building. So I guess they really wanted to dumb it down for the casual player cause who wants to think about stat and skill trees. There aren't any, so not much point in making more than one of each character type. Oh and by the way, respec =/= no stat and skill points. I'm a big fan of respecs, but what that does is change from one type of skill build to another skill build. Not remove skill builds entirely.
4) Itemization - is rubbish. I guess it's been discussed a million times. There is no scope for items like wolfhowl from Diablo 2 which does something really unique and has whole builds around it. Everything is just +stats and DPS
5) Trading/Action house. So first, they reduced the drop rate of items so low that you absolutely had to buy stuff from the Auction house to progress in the game. Then they removed the auction house, so you can practically not trade. So yeah, I guess they don't want the players to decide whether they want to trade or not. Either you have to, or you can't.
6) PvP. See I don't really care much about pvp myself. But a lot of people do. There was so much potential here, to have balanced pvp, arenas, team arenas. Guess what we got? Extremely limited, unbalanced 'dueling' after a long time..
7) Story/atmosphere. I know a lot of people don't care about this. But honestly, I don't see why it had to be so bad either. Some of the dialogues are really facepalming ( you have defeated .... but you can't defeat ... oops you did .. Seriously? ) and the entire plot doesn't make sense.
8) Graphics and sound. Ok, they did a fairly good job here, I'd say. It is the only area where it could be said to be an upgrade over D2.
there are probably more but I'll stop here. Point is, Diablo 2 HAD all these features. And some of the other ARPGs like Torchlight have most of the features.
What the D3 Dev team insists on doing is shoehorning a player into playing their own, limited version of the game instead of leaving it to the player to make the choices. Everything is, you CAN'T. You CAN'T play offline. you CAN'T mod , you CAN'T trade, you CAN'T make weird builds like dual dream melee sorcs,you CAN'T have a weapon switch, you CAN'T pvp..... Only do whatever we tell you to. Great Fun!
I really pity the schmucks making the art design of the game. It is practically wasted, because people who are calling the shots are clearly limited in their understanding of the game. They only saw the flaws in Diablo 2, not the successes, therefore they built a totally different game which is basically like an arcade game featuring 'clicking buttons' and 'smashing monsters'. Yes, that's just how superficial they are.