So I am really confused about the opposition in Syria? Are they several groups, varying in degrees when it comes to terrorism and extremism?

Yes there are several groups, ISIS or its remnants being one. Degrees of terrorism and viciousness vary amongst them, but they are all horrible. Of course, so was Assad.

I look on it as a necessary step towards getting an actual decent govenment for Syria, but there are a LOT of steps between here and there