Ok my experiences. Europe server is down way too often. Like last sunday most of the day. Annoying. Also few random DC:s which is annoying because it zeroes the whole area map and if you were just about to finnish like me last time. Aargh. Other tecnical problems too. Sometimes way too much lag and deaths because of it. That's when repair costs annoy me.
Diablo 2 battlenet worked better for those 6 years I played the game and it's various ladders.
I finished game normal once and then realized melee character (barbarian) really sucks in at harder difficulties some mobs are annoying enough in normal. Monk is better because it has some stun-immunity talents. But now playing couple of ranged characters and it's easy-mode compared.
Plus I noticed using two-handed weapon in melee is suicide.
I have played with banner now. Works, too bad it's same for all the characters.
If you like achi-system theirs don't always stuck. Like it didn't remember me killing 2 bosses that are always on your way. It coudn't have been DC since that kicks me out of the game too.
Also having that many gold-sinks like for bag space all your characters share is bit too grindy to me. Also loot-drops are more random that Diablo 2, Magic find works differently it just helps to find magical items, nothing to do with quality. And normal seems to pretty much ignore it. Working as indended, dunno?
Also I ended up with a lot worse gear (low lv) for nightmare than diablo 2. Seems normal doesn't drop over 25 items and I am mostly using some lv 11-19 rares. So no need to grind normal. Plus special mobs are more likely to drop good loot than bosses or rather chance goes down when you have killed them once.
It feels more like Dragon Age than Diablo. Lootwise too, I get lot of crap that I don't ever use (well first time around I was still thinking what stats are good). I miss low level sets. And I miss real legendaries. Plotwise and how characters speak it's dragonagish. It lacks certain dark serious feeling of diablo series. It plays like more general teeny action rpg. I didn't expect it to hold that true to it's origins. It's 12 years ago and activision was involved making it.
It's neat game, I am lot less interested playing it in highter difficulties than diablo 2. And thus play much less. And their server problems are really killing it. It should have been like diablo 2 with closed battlenet and separate off-line play. And why I can't name my character Zelda it's my damn e-mail name and not a curse-word. Stupid, and no I didn't get it from some nintendo game.
Given some time it's probably working better serverwise and I hope they fix itemization. Gem-crafting is waste of time. Since you get getter gems from gold-ah now than you are forced on-line anyhow. And they cost much less, and are better versions you could ever make during normal play but are normal drops higher difficulty levels. Oh yes you probably want jc for unsocketing. Blacksmith is more useful but too expensive. You are better off with well-fare sales in ah (those that only double/triple money they could have gotten from vendor).
Weapon dmg is much more important than it was diablo 2. Actually if you forget you ever played diablo 2 it's much better game. Well, when their servers aren't down/laggy as hell.