So I've had a chance to play it now. A mate came down this weekend as we'd been looking forward to it for ages and had played D2 together, so we've had a couple of sessions. This is what I think:
To start, setting up the game, considering we are both playing in the same room, has been an unnecessary chore. D3 has an issue with d-link routers which makes it very difficult to get it working as it crashes every 2 to 5 minutes. In fact, the only way I have managed to fix the problem is to put my computer in the DMZ. Labz was struggling similarly, and we went through a number of options, including tethering his phone to turn it into a wireless access point and using that connection (!), until we finally get Internet Sharing working.
You might think that this is a d-link problem, because their firmware / hardware is not good enough, but sadly I think you'd be wrong. When a company is going to install such pernicious DRM that you have to have a connection all of the time to play a single-player game (or a multiplayer game running on a LAN), you HAVE to make sure that you don't have an issue with the hardware that people use to connect to that game.
Anyway, ultimately undaunted, we eventually got it working. We're now in Act 2 Nightmare. We got here relatively quickly, because after enjoying the story, and dawdling through Act 1, we realised that the game is pretty overwhelmingly easy. With less control over health potions, and no real life leech mechanism (at least, as far as I can see on my wizard), combat seems limited to kiting, and using your abilities. As a result, I would reckon it to be a lot less sophisticated that D2. This is a shame, because the skill system and rune system actually provide a lot of variation (although the inability to specialise in specific skills (beyond the application of runes), is frustrating).
Frustrating too, is the zero cost approach Blizzard have taken to EVERYTHING. You die, no worries, you just lose a bit of durability. You socket something incorrectly, no worries, just take it out again. You made a skill mistake, no worries, just respec. There are no consequences to anything any more; you don't even lose a tiny fraction of your experience.
So sadly, as a result of the distinct lack of challenge, we started rushing through the game. We thought if Nightmare was harder, and was constituted by a series of more difficult battles, we might enjoy the story more there.
The good news is, Nightmare is a bit more difficult! The bad news is, that this hasn't rejuvenated the combat to any significant degree. And the combat isn't sufficiently difficult that I could say that I am struggling at level 34 to kill Nightmare Act 1 creatures.
My final gripe is with the drop rate. It's pathetic. There's no other way of putting it. A group of us (6 or so) that have probably accumulated something in the region of 200 hours have found 2 legendary items. And they've both been a waste of time. Without lamenting my desire to play the game sans the Auction House, how are hardcore characters going to fare that don't have access to the AH? How are they ever going to find or build anything?
The drop rate is important, because Diablo is ultimately all about taking something shiny and trying to get something more shiny. It's depressing when you miss out on so much of the planned content, and it's made worse by the fact that I am regularly replacing my rare items for magical ones, because I've struggled for so long to get anything new and I'm still wearing something from 10 levels previously. It destroys any sense of progression, and makes the game a lot less enjoyable.
So, that's where I stand. You'll see from the time stamp on this post that it's very late. I've just finished killing the Act 1 boss, hoping that I would, at the very least, find a couple of decent rares. I received 4 blues for my troubles, and it really does feel like a complete waste of time.
A reviewer here has said the above far more eloquently than I can:
http://www.rockpapershotgun.com/2012/05/18/how-diablo-iiis-solo-experience-reveals-a-hollow-game/
Be good to know what you think. I've been looking forward to this game for years, but in my opinion it has fallen down in so many crucial areas for me.