It was alright.
This flash had the makings of a good arcade style shooter. There are a few major things I would like to see improved before the final release, though. Keep in mind that I know this is only the beta. My criticisms are meant to help the final release be the awesome shooter it could be. :)
Number one thing that annoyed me was the voices. The things that they said were good, however, the sound quality was bad. I realize that you're were probably doing the best you could with what you had, but I am just being honest here. Also, I would reduce the frequency at which these phrases are heard. They are good, don't get me wrong, but they get stale very quickly when I hear them with the appearance of every new enemy.
Second thing I'd like to see changed is the character models. The ones that you currently have are good. Keep them. But try to spice things up a bit with some new ones too. Variety is your friend. ^_^
I thought the music through the game was good, but the menu music needs a lot of work. I, honestly, just don't like it.
Other minor changes I would like to see would be a reload time (you are using a six shooter after all), better hit detection, and, maybe, a penalty for dying (like restarting at a checkpoint).
But, despite my criticisms, this was a good game. I had fun. ^_^ OH! Also, I would like to see the steampunk theme incorporated more into the background of the levels. I noticed the cyborg arms on the baddies and the metal siding on some of the buildings, but there was nothing that popped and made me feel as if I were in a steampunk setting. Anyway, good game, needs work, though.