Pros: The running and gunning is fun and flows nicely, enemies seem to spawn more aggressively in certain places, music is pretty nice and the game has some nice gender customization with the female parts and hairs which is a step in the right direction. So a little advice would be to try to make the next batch of "Female" parts a little more than "Mid section with tits" or Heels. Think outside of the box a bit.
Cons: First off it's a pretty graphically intense flash game, lots of gore and permanent particles flying everywhere. So it makes no sense to me to not have ANY graphical control for the players. It was in every other Thing-Thing (that I recall) and worked fine, so why not in this new one?
Guns need to be unlocked; I feel like the starting weapon of a player is very important to most, a little more choice would be nice.