I know very little of the R3R group. But i enjoyed this...
I have a few suggestions.
1) The aiming seemed abit off. So if another game was made like this. I would suggest you make it to where i can shoot easier.
2) It would be nice if more enemys came from different directions. Such as dropping in from air planes and such.
3) Listen to some of the things Clock-Sgt suggested. :P