Moonbase 332 (Steam key/Region free).

http://store.steampowered.com/app/397580/
Hello and Welcome to Moonbase 332
Moonbase 332 is an Arcade First Person Shooter by PatchNoteStudio. You play an old American exterminator. After a War between Germany and Austria in Year 2007, a base on the Moon was found. Austria has tested there some genetically modified Plagues to use it as a weapon. Your job is now there to clean up. Fight your way through the Moonbase 332.

5 Chapters, Each with 5 levels (includes boss battle, bonus level, etc.) (25 Levels)
An absurd story (+Cutscenes)
Some secrets (hidden weapons, items, rooms, etc.)
The difficulty level varies with the player behavior.
Liquid gameplay with up to 60 FPS
The game speed increases with each level
Health regeneration does not exist
Ranking System and Online-Highscore list*
Lifetime free updates*