Swen mentioned that the released content is about 20-30% of the final game, this depends on your play style though.
I sure hope not. That would make for a *very* short CRPG. I wouldn't be very happy if that's the case.
Here is the source, transcript of the Twitch TV session:
http://www.larian.com/forums/ubbthreads.php?ubb=showflat&Number=484842#Post484842 (search for "final game")
Now, the content in Cyseal is about 20-25 hours long depending on your play style. So, the final game will be about 60 - 80 hours long (again depending on your play style).