Not a bad game. Violent without relying on outright gobs of gore, Difficult enough that you need to strategize to make it anywhere, and no slowdown that I could detect. I do have to report that monbyol's results are at least semi accurate, in that even though I pumped damage every level for 1 through 13, the amount stated on the levelup screen stayed constant with the ammo amount and didn't seem to change damage in a hidden way either.
As for the perks not working, I think it might be more that without any sort of numerical indicator the effects are almost too subtle to notice, such as possum only giving you back partial health so you don't even notice when it triggers. Maybe a future update (or sequel?) could show a number for the rounds you have left/trigger a sound on possum's usage (the same sound played when you pick it as a perk?)/etc?