For a little history of what Shin Megami Tensei is, well it is amazing. The story is the better than any television drama. Trust me, go out and buy Shin Megami Tensei: Persona 4 (or 3 FES) and the game will blow you away. The game play is typical role playing, but there is so much to do within each game it is a crime to not buy one of the titles.
As for Shin Megami Tensei: Imagine Online, I have no idea what to expect. I was reading a PC magazine story on it. You and everyone else playing is in charge of restoring a destroyed Tokyo. You will be helping the restoration project by completing quest and powering yourself and your party. Your party will consist of demons and humans alike.
The combat is real time (ugh) and that you can be attacked anytime. As in while talking to an NPC (non-player character) you could be attacked, but that is what the magazine said. I believe that being attacked anytime would kind of be harsh for people not used to Shin Megami Tensei games.
Core elements like fusion make an appearance here. You can mix and match different demons to create new and most likely more powerful types. Also a system for finding friends is built-in the game allowing you to find people bases on a pre-determined criteria.
Personally I am excited. I hope that this game does not go the route of Tabula Rasa. Then again if the game does fail out in the states, the Japanese base is strong enough to support the game.
You can play the open beta now for FREE.
story at http://pc.ign.com/articles/941/941232p1.html