Ok, first up I love the film. It's one of my all time faves. It travels along nicely with classic "end of chapter" cliffhanger lines such as "If it bleeds we can kill it" and "something's out there waiting for us, and it ain't no man". The action and the pacing of the film are excellent, and despite what the plot is, it's done so well that it's almost believable.
The reason I'm only giving it four stars is because the blu-ray transfer isn't really all that great. It is slightly better than the DVD, but as stated by another reviewer the source material was already a little grainy and the High Def transfer seems only to highlight this further. There are also no extras unlike the DVD, so you really aren't getting value for money. As Blu-Ray's go, it's not one of the better ones, but I love the film so much I can just about forgive it for that.
In short, if you've already got the DVD (probably available for about £3) then you're not likely to feel that you're getting your money's worth here.