So, I recently got into the Diablo 3 EU beta and wow. Seriously, wow. This game is BAD. I'm shocked it managed to get past even the new Blizzard's QA team.
I'm getting 200ms ping and having that registered as "good" (ie. in the green in terms of latency) by the game, with random 500ms lagspikes. It's entirely possible that the EU beta's servers are set up in the US, but I get at least 160ms from US servers in every other game, and god only knows. This leads to a shit tonne of artificial difficulty and near death experiences.
The CoD-esque levelling mechanics are laughable, as are the ways abilities work. Every level, you get a new ability or a new upgrade for one of your abilities, and you will ALWAYS have every ability at max level. You have no choice in what order you get them. The only thing that distinguises you from other players is gear.
Switching out abilities gives you a 10 second (or thereabouts, not sure on the exact figure) cooldown on that ability, which means switching out abilities or having more than six active abilities is unfeasible, which can lead to situations where you get attacked and don't have the right ability for the situation.
All this just feeds into having the easiest general loadout and spamming the attack until everything is dead, regardless of the situation. You approach everything in the same way, deal with it in the same way and the like. You won't vary from other player's experiences either, as they're ALSO doing it in the same way.
Don't get me started on how horribly the classes are in general. They're not archetypal, they're not very balanced (heavy armoured barbarian / monk more easily kills stuff than the flimsy wizard?) and they're just not very fun. Witch Doctor is a bad necromancer clone, Demon Hunter is like a crappy D2 assassin, Wizard is just a poor man's sorceress, Monk is actually alright in terms of overall design and Barbarian is just a straight rip from D2 and therefore the best class in the game.
The healing potion / healing orb issue just shows how schizophrenic the design team is. On the one hand, you have healing potions which allow you to decide when you need healing and use them when you need them. On the other hand, you have healing orbs which drop randomly off mobs and heal you when you walk over them. Of course, due to this, healing orbs are utterly useless, or at least could be better replaced by healing potion drops, and is a fine example of "lol wut are we meant to be doing again???".
Graphically, the game is horrible. It reminds me of Icewind Dale 2 in terms of looks. You could say it has a certain style to it, if you thought style could mean "looks like it's from early 21st century". Low polygon models, ugly arse textures and a general bad colour scheme just makes the game seem faded and already aged. Compare it with, say, Diablo or Diablo 2 in modern resolutions and they don't look nearly as aged as this game.
Controls-wise, the game's okay-ish. Everything's pretty much the same as Diablo 2 (shift to stay still whilst you attack, ctrl to view thingies, alt to view items etc), and everything is therefore okay.
I just fail to see how this is a Diablo game. To me, it feels like a poor Korean Diablo-wannabe that made a bunch of bad design decisions because they had a massive budget, a lot of time and no idea how to improve on the original.
The graphical changes, gameplay changes, EVERYTHING changes have just ruined the overall experience and turned it into a game worthy of nothing more than the award of "Worst AAA Game of 2012".