I thought it was good, but not a perfect ten good. Normally I'd have rated it a 7, but I gave it an 8 in fanboyish goodness. It would definitely be a seven, maybe even a six, if I hadn't seen the show. There are a lot of scenes which really resonate having seen the show, but probably wouldn't if you went in cold. I'd go into more detail but this is a spoiler-free thread.
Personally, my feeling is it would have worked much better as the second half of the first season, and maybe that's where Joss was going before being cancelled, who knows?