My idea of a Diablo 3 would have to take place maybe 20 -30 years after Diablo 2. Due to the worldstone being destroyed, a crack is formed between dementions. This will cause the two dementions to be tainted by the other one (our world and the realm where the prime evils are from.)
Shrouded in perpetual night their are more monsters running around, some have even become allies to our cause to see the two relmes return to normal. Due to this you now have a choice to be either a human or monster character, both with pros, and cons.
The game will be split into 2 major acts each consisting of eight quests. The first act will be earth bound, while the second act will be within the worldstone.
The first act could have a quest to save Harrogoth from invading demons within the town. You must hold off the invasion for a set period of time, in order to advance. Another quest could be to find "Cain's Book of History" to figure out how exactly you can get into the worldstone and what to do their. His reamins could be a type of shrine to some lesser demons on this world. To cross into the worldstone, you need a guide. Unfortunitly this guide is being pitted against a horde of worriors in a battle arena. With this quest you must defeat 2 human hero's, at the same time. Both are random character build types (Zealot, Hammerdin, Blizzard Sorc, Bone Necro, ect.) After aquiring a guide, you venture into the wordstone, and begin act2.
Once you enter, you are faced with a upside down mirror image of our world. Everything is backwards EVERYTHING! As powerful as your gear is in our world will make it that much more cursed. Every strength you had is now your weakness as far as gear goes. This means that not only must you have godly gear in our world, but another set of gear for the worldstone world as well. (Maybe have this world where runewords are not effective here or something along those lines.) Here you get another skill branch to add on a whole new group of skills and powers.
As far as surrounding go you could have a swamp land, where movement is lowed by half ,or even a area over a river of blood with one long single path bridge. While walking across this bridge you are attacked by creatures coming out of the water. Another idea could be a area where the air is poisonous, you take damage every second your within this poison cloud area unless you have good gear to counter it.
A good quest to have here would be a mirror match, where your character, and group are copied. You are then forced to fight them to proceed further. (intersting spin on a PVP game) This could be the equivilent to the ancients maybe.
A ending that could be intersting would be, a currupted Tyriel. Have him have the skills of any mix of player characters, and to add to that all the prime evils powers to boot.
Within this game you could have a seperate area to battle as PVP, and, or have a area of a town full of merchents who sell all differnt types of items depending on the person. Also a few NPC's that could sell you demon slaves as mercs. It would be nice to also have an area to stash all items found that are not in use. Even though "Mules" are not indorsed by blizzard, it still would be nice to have.
As for playing this on a battlenet styled enviornment, after beating a HELL level you will automatically be placed in a Hardcore version of the game known as Purgatory. If your character dies here then it is gone for good just like in hardcore now, all the gear is gone as well. You can find a hidden level in Purgatory like the cow level now, but it will be a one on one contest against a monster, after defeating it you get a harder one, and so on. Within this hidden area you can aquire any and all items and gear. Unfortunitlly you will be faced with every creature within the game, and since its hardcore, you can still die and loose everything you have. WHAT A CHALLENGE!
Please forgive the grammer I can not spell to save my life.
