When you complete the 4th act, you will unlock the next difficulty level for that character. If you finish on the hardest, Inferno, it just congratulates you. You're free to keep using that character and redoing Inferno for better gear, or start a new character, etc.
Yes, Diablo is in Diablo 3.
Yes
No. There are Diablo 3 teaser videos on the Blizzard website.
Mephisto is mentioned, but does not appear 'in person' during Diablo 3.
Diablo 3 is out now, it was released on the 15th of May 2012.
http://www.glu.com/blog/super-ko-boxing-2-strategy-guide use this address to find details how to beat el diablo
No, there is no pirate class in Diablo 3. If you mean to pirate the game, you cannot do that either.
diablo 1 is about 100mb diablo about 800mb and diablo 2 expansion another about 800mb
When you beat the campaign you unlock ratchet and shockwave.
It's been over 13 years since Diablo 2 was a true Hype, so this would give you a perfect reason not to worry if Diablo 3 would be your 1st Diablo game experience.
The requirements can be found at the official Diablo III website.
Diablo 3 was released on May 15, 2012.