1000 polies for something that will be taking up a quarter of the screen is definitely not overkill. I like the design, kind of a mix between the quake 2 and 3 grenade launchers. Im not a big fan of the grey blue and red colour scheme though.
I think the handle is too thin. Also, where do you put your other hand to steady it? Just underneath? Usually there's an underside grip as well. The color scheme is ok, not sure if paint would hold up in combat situations. JKMakowka - 1000 polys is fine for weapon models, if the power exists it should be used.
The mesh looks really nice, but I still think 1000 polys is overkill for weaponmodels, even with todays fast computers. That computing power could be much better spend on other stuff. Oh and I really don't like that red on your concept pic... dunno but for me even fantasy weapons should look like 'realistic' weapons.