Actually. I lied. A little. It's not as humungous as I thought at first. While there are still around 15 planets, most aren't very...in depth. They are basically planets you just drive around and shoot things in your little rover and scavenge stuff. It's really fun at first but it can also get pretty old after a while. And it's all in the milky way galaxy. But there are about 10 (maybe more) clusters/nebulas you can go to. And in each one there are 1-5 solar systems. In each solar system there is usually only 1 planet you can actually land on. But you can survey some other planets. But there some just sitting there as well that I am guessing might become downloadable content. But so far, I know of 5 different planets that would be equal to the length of the kotor planets. Regardless of everything, everything is done extremely well. The only problems (I don't know if I said this already but i want to reiterate) I have are shadows on faces when in chats and glitching when running or hitting walls or stuff like that. It's soooo good. Though. I played it until 4 this morning and just can't stop!!
I don't know how to describe the engine but the enemy is Saren and his army of synthetic geth. He was a spectre, working for the council, and he betrayed them because he knew the end of the world was coming and wanted to try and save himself instead of fight and resist. And you need to go and try to stop him and the machines coming to "cleanse" the galaxy. I don't know of any more to the story yet because according to the achievements, i haven't completed the majority of the game.