My opinion is, if it is better than the Eragon movie, I'll be happy (well, it can't really be much worse...). However, Eragon is not on the level of asoiaf, so that could be the difference.
The thing that always makes me mad when books are adapted is that no one seems to look or act like they're supposed to. Maybe I have a wierd type of ocd- it just really bothers me when the book is misrepresented.
Oh, and if the show is a flop, won't people assume that the books are crap too? I can't decide, cuz I'm kinda like you AU- I don't like it when things I envision as my own 'discovery' become something that everyone knows about.