Yes, there is a preview of The Sims 2 at The Gamers Temple. It's the first that exists, even before any official announcement from Maxis. They say it will be in 3D ("get an underwater view from inside a hot tub"), Sims will age, there will be pets and downtown, old town and vacation island will be included in the game. There will also be a couple of new pets like horses etc. And: evil Sims:

"Now for one of the really big changes – your sims will now have a good/evil character trait. Good sims will behave a lot like sims in the current game, but evil sims will be a lot different. Evil sims enjoy homes filled with trash and broken objects, and must work to keep their relationship scores down with good sims. The more good sims that they have a rotten relationship with the better. To help evil sims out, there will be plenty of new evil interactions. Some will be simple slaps and bullying interactions, but others are going to be a lot more interesting. There is a pretty tight lid on what these actions will be, but we did learn about the “spread vicious rumor” interaction (particularly effective against sims that are trying to build up a good fame score). Good sims and evil sims do not get along, but evil sims will need to build relationships with other evil sims. Evil sims can marry and make little evil families, but if they build a high enough relationship with another evil sim you can use the “leave spouse” interaction to break up the unhappy little home. Finally there will be different career options for each type of sim. For example, only evil sims will be able to become career criminals. Both evil and good sims will be able to enter politics, though."

Too bad it's only an april fool's joke... But nevertheless, you might want to read their ideas (and post your own) right here.