I think Legion is the best new character in the game. I was excited when I heard on the old boards that there was chance that Legion could be recruitable. Now that I have met Legion in ME2 I wasn't disappointed. Very cool.
On the old boards a lot of people thought that all geth were evil. I wasn't convinced, because that didn't make sense to me. So, I started a thread on the old boards that had a simple basic reasoning. If geth are sentient and are capable of creative and independent thought then there must be geth that are not evil. I also thought that the geth's religion was a form of the reaper's indoctrination. A lot of people didn't give it a lot of attention and the thread never got many replies. It turns out that I was very close once Legion talked about the heretics. That was cool.
I was also wrong about some things. I assumed that most geth were evil, but there would be geth that opposed that. Legion might be one who was part of an organized resistance. Hehe. Ah well. You cannot be right about everything.

I also went a bit over the top and dreamed that one day the geth could get a seat on the Council. I completely forgot that they might had to start peace negotiations with quarians first. Hehe.
One of the things that a lot of people still think is that geth don't create other geth. They assume that they are build by... I don't know... the quarians? But the geth have now an evolution on their own. Geth build other geth. They are able to improve their own programs and they do. They create new variations of their own species. And thus they have a real "evolution".
Often people think that the geth are somehow ruled by Asimov's laws of robotics. I don't think that is true, for the simple reason that they are not created to serve their masters any more. They are their own masters. Also, many scientists believe that Asimov's laws cannot be implemented. They also believe that it is hard to control the friendlyness of artificial intelligence by "programming".
If you are interested in the subject then have a look at the follwing article:
Friendly artificial intelligence.