Downloaded and tried this a while ago, forgot to post anything so...
I'll not go in depth but a couple of things stand out, apart from the time you've put in...
The grenades...link them to the gravity so they arc, or turn them into missiles, they just don't look right.
I would say the biggest thing you need to address is the visuals, normally I would never say that but here everything looks very flat and it takes away from the immersion. I am assuming from the models you use SU, you can apply decent textures and bumpmaps to these and it would make all the difference, even if its takes a little time. if you want post a model, eg the robot or the house or something and I'll make a quick mod to show you what it could look like in Rad using some of the very simple, free, techniques I've posted previously on the forum.
The beginnings of a decent game but needs either more action or to look prettier to hold the players interest. Keep up the good work