This is the best browser FPS i have EVER seen. It even beats some downloadable ones :). I suggest that:
1. there be customization for your in-game character
2. A firing range
3. A better tutorial (more in-depth about all the features)
4. A client or make the maps downloadable from somewhere else (I've been having some trouble with that)
5. More servers, especially for lower levels (this game is, evidently getting more popular so its hard for me to find an available match)
6. Clean up the shop and home page a little
7. Keep doing what you're doing! :)