1.0 release version. Truly the best hl2 experience ever
To install this amazing and best mod, simply drag "beta_man-problems" folder to sourcemods folder (Steam/steamapps/sourcemods)
Install Source SDK Base 2013 Singleplayer (you can find it in your steam library), go to it's properties (in steam), select "Beta versions" and change it to "upcoming"
You can finally play Gasmask Citizen 21, good luck.
Have fun playing this uncool mod