Diablo 3 is coming out on May 15th. The official forums are awash in cries of ecstasy and exultation liberally mixed with questions from all the sensible folks who haven't spent the last six months trolling the forums and playing the beta over and over. The game sure feels close to release quality at this point so Blizzard having two more months means that it should be absolutely rock solid when it finally does hit the shelves. One really huge advantage of having online only play is that even if they print the DVDs a month in advance they can apply patches right up to the day of release to optimize the experience; it certainly gives them a little more freedom to push things out aggressively without worrying about quality.
The latest iteration of the beta is challenging. Not hard enough to kill me, certainly, but hard enough to force me to play well, minimize my damage and drink potions now and then; this seems appropriate given that I have thousands of hours of experience and they want the game to be beatable by random buffoons! In the initial push of the beta D3 was so utterly trivial that it could be easily beaten without gear of any sort aside from the starter weapon and now that would be extremely difficult. It makes me very hopeful that Inferno will be hard enough to really challenge good players. People with little skill are going to die sometimes in the first part of Normal and in theory the game gets harder in Nightmare and harder yet in Hell and Inferno; because only the really hardcore gamers are going to be farming Inferno Blizzard can feel free to make it soul crushingly difficult.
The balance of the current version is pretty decent but there are still some problems. Some of them are due to only having four skill slots in the beta instead of the six that will eventually be available. You can't have really niche abilities make it onto any of your four slots when you have multiple types of targetting (AOE, single target) and multiple resource usages (generate resources, use resources). This means that Blizzard needs to push the niche abilities like Preparation (a Demon Hunter cooldown that restores all of your Discipline) later in the acquisition queue so they line up with getting the fifth or sixth skill slot. There are also some abilities that are flat out useless because their numbers simply aren't high enough like Explosive Blast. This latter group is going to be very easy to fix though, simply raise the damage value some and viola.
There are a few things about the game that are really different from D2 that are going to be very difficult to properly test however. The biggest one to my mind is the way quests work with multiplayer games - your game has to start on a particular quest and people join up for that quest. If you are trying to do a quest that nobody has a game for you can't join up and do it as it will either be locked out or already complete in their game. This means that everybody in a game has to be on the same quest and has to work together unlike in D2 where players would regularly join games with the intention of completely ignoring the quests and zones the game creator was interested in. I think this is probably a good thing and will lead to people cooperating and finding groups effectively but it is hard to know how it will feel without really testing it live. We can't test it effectively on the beta because it is so short and mostly people all just want to do the final quest over and over to get loot.
The other thing that is very hard to test is the way trading will shake out. There was absolutely nobody that predicted that the Stone Of Jordan (I have leet barb tabar for 1 SOJ!) would be the currency of D2 but it certainly ended up that way. Until we see the entire economic system in action we just won't know whether or not the costs of the Blacksmith and Jeweler training will work and how the endgame item economy will look. Given how much fun D2 was even with its utter disaster of an economy everything will probably be fine but we just don't know!