
Hello my friend, stay a while and... Now is not the time Cain. (/snicker)
Only 5 classes. Witch doctor and barbarian make two. And you can select male or female now, which is a great feature. I'd guess the sorcerer and amazon are likely to make their return again. Melee, Ranged and Caster were the primary classes in Diablo 1 and also present in Diablo 2. Druids in D2 sucked, the necromancer was fun but rather weak and the assassin sucked badly as well. So what would the fifth class be. Paladins again, or something new? Time will tell I guess. How about an evoker? Changeling? Maybe druids will be back after all.
Beginnings
Diablo, it didn't even have a number back then, was the first pc based RPG that I've played. The atmosphere when you entered the cathedral the very first time is something you'll never forget. Dark, creepy, mysterious. It set an amazing theme straight from the beginning of the game. I think I was still using a 33k6 modem back then.
Diablo 2 was released, obviously I got it, and the expansion pack as well. The game was good, and enjoyable, the atmosphere was there, but much different from it's prequel. Diablo was supposed to be a dungeon game yet D2 took place mostly in grassy fields, deserts, and forest jungles it just wasn't the same.
With new times came new internet, an unlimited and fast DSL connection. This opened up Battle.net, a free multiplayer network by blizzard and all that came with it.
Diablo 3 had better have an awesome atmosphere. (Which it does seem to)
Diablo 3 had better not have me running across deserts again.
Diablo 3 had better still be "random". Because random is good, it gives replay value.
Hacks and cheats
Battle.net, while good in concept fails horribly due to the pathetic community of players that it houses. Scammers, ninja looters, hackers and more. Item duping, item hacks, fake items, there just wasn't really an end to it. And there wasn't anything that blizzard was doing about it. Why would they? You pay a one time fee for the game, and they give you the option to play the game across battle.net which is about where most support ends.
Diablo 1 had town kill PK, open PK, item dupes without needing software.
Diablo 2 had less hacks and software exploits, but dupes and hacked items were plenty around. Stone of Jordan anyone?
I'm sure Diablo 3 will be a great game, but since the game will allow single player mode, offline play, and open battle.net it's only a matter of time before every cheat that was available in Diablo 2 will find it's way into Diablo 3.
If blizzard wants to score big with Diablo 3, they'd have to set up an active subscription and GM system much like they have done in World of Warcraft. I don't mind paying some extra cash every month, if this means my game remains free of hacks, scammers and exploits.
I never gotten any of my accounts hacked, many people I then knew did though. This was a big failure in battle.net though understandable since it's hard to keep track of your friends otherwise. They sure tried though, I've logged on at times only to see a big red warning from battle.net : "108 failed log in attempts since you last logged on". It feels special. I wonder if the Blizzard anthenticator will be useable for your Diablo 3 accounts?
Diablo 3 had better have cheat prevention.
Diablo 3 had better not have me whispering people based on their account name. A special whisper alias would be much better.
Trade me this

How would you get some good value for it? Battle.net has a trade channel, oh jolly oh em gee. Is that it? Sadly, yes. A trade channel where about 200 people (if not more) are trying to spam (every single freaking 1-2 seconds) their wares for the lowest price, because obviously their stuff is the cheapest, best, non hacked item that you could possibly find. How much does your item cost? Only 40 duped Stones of Jordan good sir. /sigh
Alright, so you sell some stuff, got 20 SoJ on one of your half a dozen mule characters. Perhaps you even had two or three accounts. (Or 11, like me...) and you found what seems like a good deal. Somebody selling a lightning enchanted charm. (1-24 lightning damage 1 bag slot, if you don't know what I'm talking about, just go with it ok?) Or perhaps a grandfather (large unique gold colored sword). So you agree to meet the guy in a private game, he opens up the trade window and puts the item in there. You check it, and indeed it's the item. He moves the item around a bit (this is because of a certain hack which allowed players to put a "fake" item image into the trade screen), and at the last moment switches the item with a different low value one that looks exactly the same and presses 'ok'.
You got scammed.
It's better than it was in Diablo 1 at least, there wasn't even a trade screen then. Just drop the item on the ground and hope the other player doesn't have a town-hack and can teleport or something. Which is one reason why I never really traded much, too much risk. I just made more accounts and stored anything and everything I ran into that was somewhat interesting. I had some friends that were the same, and we traded mostly among each other.
Diablo 3 had better have an auction house.
Diablo 3 had better have a damn big bank storage space for all my crap.
Free for all looting

The World of Warcraft group loot: need / Greed and master loot systems are great. Sure you can get people to roll need if they don't need something. But that's easily remedied with public shame or guilds. The free for all loot system from diablo however, is one of the main reasons I'm not looking forward to playing on battle.net again.
Diablo 3 had better have a group loot option.
Death penalty
In Diablo 1, if you died all your gear would fall to the ground. Good luck getting it back. That game was hardcore. Frustrating, but fun. It also gave a whole new dimension to player killing.
In Diablo 2, if you died, you spawned in town and had to run back to your corpse. Only your first corpse had all your stuff. If you got back a little, but died again on the way there, you were screwed. If you logged out your corpse would be just outside town though.
In Diablo 3, well, we can speculate but hopefully they will implement a "ghost" feature like world of warcraft has. It's for the best.
Diablo 3 had better not have me fighting to reach my corpse.
Diablo 3 had better not have lightning enchanted multishot creatures.. (Seriously)
A new game
But still, one shall need to try it. Bring some world of warcraft buddies along, start a guild, play with friends, slay big demons, complete nightmare and hardcore mode. Ya know, for good old times' sake. Meanwhile Blizzard has learned a lot from D1, D2 and several years of World of Warcraft. Hopefully these new findings will help them make Diablo 3 a truly enjoyable game instead of the piss hole they turned D2 into. Just look at the recently created Diablo 3 forum and tell me what you see. A pitiful heap of annoying 12 year olds screaming at each other, /shudder. If D3's online component were subscription based like WoW is, this disgusting cesspool would decrease dramatically.
Speaking of guilds, at the release of D2 we were promised there would be guild halls and everything at some point. Perhaps they will be implemented into D3 properly? Would be nice.
So, will you be getting Diablo 3? There's a poll on the right.