Bad Really, really bad movie (and I don't mean that in a good way!). Gabriel had no plot, poor dialogue and what storyline there was lacked depth - I'd like to blame the actors but that wouldn't be fair because it appears that they really had nothing to work with in the first place.
Special effects on their own cannot make a movie hit, they will always be a supporting product that can only be used to bolster a good plot. In the case of Gabriel any plot at all may well have helped remarkably.
Loved the swearing - if there was an award for gratuitous swearing this film would certainly have won it; the 'F' word really helped to disguise a lot of very poor dialogue.
Summing up; I believe that a primary motivator here was a sort of "build it an they will come" philosophy with regard to some outstanding special effects. However, in the context of this production as a whole the project must be considered a failure in that they did indeed build it but I can't help feeling that nobody came.
As an afterword I think I should point out that in general I like this kind of movie. I really enjoyed Aon Flux and the early Matrix movies and even the first couple in the Alien series but Gabiel was flat, shallow and confusing.