You know, I think I have to disagree (and I paid real human money to see it in the theaters)! As a huge huge huge Eisner fan, I think it's certainly coming through a really thick, really weird Frank Miller filter, but I felt a lot of Eisner's Spirit in there.
I don't think Will would have had any interest in a straightforward Watchmen-style adaptation of his work, especially considering how varied and all-over-the-place his Spirit stories were. I mean that both in terms of actual types of stories he told using "The Spirit" as a vehicle, and the art styles. (Kyle Baker had a GREAT post on his blog about this that seems to have gone missing).
I liked the movie a lot (uncompromisingly weird-as-hell, great great visuals, some really great lines), but I didn't love it (those awful henchmen!, a lot of the acting, I really did want to see the blue suit). I'm glad it was made, if only to get a glimpse inside Frank Miller's crazy-go-nuts brain. It's good to see he had the stones to just do whatever he wanted with the movie and not worry too much about reception.
Also, Stupornaut - There are a couple "Best of" Spirit collections out there, and the archives are usually around $15 used on Amazon. Kitchen Sink did a pretty good reprint run, and I've seen tons of old issues out there. I'm actually about to get rid of some Spirit reprints in a mass comics purge, PM me your address and I'll mail you the couple issues I have.