it could be really great..OR REALLY CRAP.
Since I've forgotten a lot of the book it wouldn't be so bad. I wouldn't want to read it again for the film though, as I Imagine they'd cut out important parts.
Only thing I worry about is it might start quite slow(kind of like district 9), not necessarily a bad thing but it might cost it reviews. Depends on how much treatment they give of his childhood(the experiments n such) and his training before getting the Spartan armour.
Also Not sure if I'd prefer real actors or a very realistic CGI experience(but you can tell it's not real people).