I think it is up there with the best of all time. It really has it all - complex story, depth of characterisation, awesome special effects, surprising plot twists and a healthy measure of good old fashioned violence.
I would say that the one thing it lacks is humor, now I know their in a pretty humorless situation but even in the most morbid situations we humans like to have a bit of a laugh. Other than that, Brilliant. Amazing to think that this was derived from a (lets be fair) not very good show from the 70's with one of the head writers from Startrek DS9. Who could have predicted that it would work out? Have you checked out "Heroes" yet? Whilst not on a par with BSG it's getting pretty damm good.