Male, 0.200 seconds to react
It's a nice idea, but I think the game is a bit too simple. This is really too bad since I can see that you put a lot of work in the graphics. You said that this was 'in the name of science', but I don't really believe that. I also don't know why I have to give my name, are you going to make a high score list or something? It's a bit pointless to me. Anyway back to the game.
Like I said, the game was a bit simple. You put a lot of work in the graphics while it's just shooting that guy and you're done. I think it would be cool if you added more enemies that just come out of all kinds of places, from behind the cactus and such. You have to shoot those guys and it will say your reaction time somewhere in the top corner or bottom corner of the screen. Then you have to shoot a few more guys and at the end, it'll show your best time. The game is a lot more fun that way. I would also change the music if I were you. The current music is alright for the game as it is now, but if you use my idea, it wouldn't really fit, so choose something different then. Some more guns would also be cool, you shouldn't add machine-guns of course, but handguns are alright. My last idea: add something so that we can also shoot other things, like a hole in the cactus and stuff like that.
Overall 6 out of 10. I'm not sure if I voted 2 or 3, but I saved your little game. As I already said in the title, I'm Male and my fastest reaction time was 0.200 (the first time I tried it was 0.24 or something). Anyway, the game was alright, but I hope you'll expand it a bit and resubmit this someday. Keep it up and good luck with the 'science' (maybe you should post the results on the BBS).