I think what immediately draws me to anime is the animation and character design.
What keeps me is a good storyline and character development.
I'm not saying that all anime has the above - or that if it has one of them then it has the others - but a really good show or movie will have all of those.
Anime is also very good when it's original but I despise a lot of the stuff that's out there and follows a cookie cutter plot and has all very generic characters and twists.