I thought it was a bit of a mixed bag (Mr Ber, who watched it with me and is almost as much of an Alien fan as me, was far more impressed). Some bits were awesome (David and the holographic orrery, for one - no, scratch that, David him(it?)self), but some were just as silly as some of the worst grand guignol moments the later Alien incarnations have produced (I'm looking at you, hybrid Alien baby in Alien Resurrection). The idiot scientists really, really annoyed me.
The best review I've read about Prometheus is by a friend's husband, Cavalorn; you may have seen it elsewhere, as apparently it went viral!
http://cavalorn.livejournal.com/584135.html