This looks pretty good. I like the model itself, and the detail you've put into the texture.
I have to pick on the variation of the scratches though. it looks like this thing has had a pretty rough time, due to its flaking and loss of paint, the steel is eroded a little, etc. But.. I see no wear and tear on any of the obvious places.
Around the front, and the sides, i would expect to see damage to the corners of the steel, especially along that front blue painted face at the bottom, I would expect to see some damage as if the wielder of this weapon has hit it against something, or smashed it into someones helmet, etc.
The laser firer itself looks pretty good, maybe some lengthy scratches along the canister, as if it's been drawn over and over, or laid down on its side when the character is doing something else like looking through a cabinet.
The grunge itself looks excellent, it definitely says "Warehouse/underground" to me, a sort of Alien shooter, or zombie shooter, maybe even something like Fallout 3. But the one thing that I noticed straight away was lack of wear and tear in the more obvious places.
Other than that, I would have to say this is a freakin' excellent weapon. It looks fantastic.
Brilliant modelling and it looks very realistic in design, as opposed to the stereotypical kind of shiny silver sci-fi laser guns. I really like it! I can't be the only person who really wants to own this as a prop?