Well error 37 trying to log in now. Hurray for primetime.
They talk a lot about "Blizzard-level" of polish that they put into the game, micro-polishing for the last 2 years etc, but they ended up shipping a UI that is sloppy and terribly designed. They could have done a lot better.
For example, I didn't even notice the "server shutdown" message (probably because I'm focused on staying alive, not on text). Ended up getting booted mid-dungeon, luckily enough not in a dangerous situation. You'd think they could do something like pause the game with a giant modal dialog until everyone clicks to dismiss or 1 minute has passed (aka: like the boss encounter dialog) so that I know to get my character out of harm's way.
There's so many things in the interface that could be way better. For example, when I have the quickjoin options I have like 20 friends online, so up to 20 games...at 3 games per page. And none of those games show details without me hovering. And they seem to be unsorted (or at the very least, hardcore and softcore are not separated). And in order to scroll in the list I click arrows instead of having a scrollbar. Would be better if instead of this nonsense we had something like a little chart with things like 1) quest 2) friend character level/class 3) game type (HC/SC, private/public) and difficulty and 4) current party size. Then it should sort the currently selected character's current game type up top, then by quest.
Furthermore, even the friends list display is substandard. I can only see like 6 friends in a single page despite running 1650x1050 resolution. The friends are sorted oddly: At the top, realID friends without battletags (ie if they don't play Diablo3), then by BattleTag for realID friends, followed by non-realID friends. I can't tag my friends or separate them into custom groups, so my work friends are mixed in with my WoW friends, my FFXI friends, my other online buddies, etc.
When the friends list is open, it overlaps the profile window when I go to inspect one of my friends. In order to view the profile window unobstructed I have to close the friends list (the profile window cannot be dragged around) which then if I want to view a different friend, I have to re-open the window and search for the friend again. I'm sure if I could log in I could list a half dozen more deficiencies that they should have caught during their 2 year polish (especially since frontend UI is practically independent, should be stupidly easy to borrow a few UI programmer from WoW or whatever)
I can't even figure out the chat channels. I managed to join Hardcore chat and there was all of 3 people in it, but I couldn't figure out who those 3 people were. No idea what level they were, nor classes nor quests complete nor if they even were playing in a game at the moment (since you can stay in channels while in-game). The chat definitely has that "ghost town" feeling that SC2 had...lots of people playing but not many playing together.
Missing having a "friend's characters" ladder tremendously as well. I can't check on the progress of my friends very easily at all, and it's a huge hassle for me to discover which of my friends have characters in the level range of my characters so that I might suggest a cooperative game.
If you're stuck at the main screen and choose to look at cinematics (because perhaps the servers are down or something!), you only can choose cinematics that you have seen on that computer. The game doesn't do a "cloud sync" on login to acquire the list of cinematics if you play at multiple locations.
Soooooo many things.