No revenue estimate for GOG — its rating/review counts don't calibrate to sales the way Steam's do. Reviews and prices only.

Brotherhood

They are billions. You are alone. An ominous brotherhood of religious fanatics perform experiments on humans in their top-secret scientific complex. An ancient prison hidden deep in the Swiss mountains houses hundreds of test subjects whose bodies are mutilated in an effort to produce a new biological species of superhuman. You are one of them, but unlike other test subjects, your body is immune to mutagens. For you, it's not poison anymore, rather a source of power that makes your body nearly indestructible.     Steal the weapon and obliterate them. Break into the depths of the secret complex, unravel the secret of the millennial brotherhood's ancient technology and harness the power of mutagen to annihilate all those who stand in your way.   A timeless classic, with a fresh presentation. The Brotherhood is a retro-shooter with classic Wolfenstein 3D style. You will feel right at home when exploring complex one-story levels in search of first aid kits, ammo and key cards, while fighting hordes of enemies in action-packed firefights. An old school shooter's classic weapons, upgrades, and well-hidden secrets will complete the experience.   Enemies are powerful. But not immortal. There are more than 20 types of enemies in the game, and each knows how to kill you in a variety of ways. Among them are ordinary soldiers, cyborgs with power armor, flamethrowers, and huge walking mechs. Fear not! There are brutal means to fight them all! A total of 9 types of weapons representing the most advanced engineering fashion of the brotherhood. You'll have plenty of obliteration methods at your disposal - not only a shotgun that can make a juicy "bang", but also a laser rifle that can fire infinitely, a flamethrower, and a rocket launcher. There is also...a " Butterfly ", a weapon so secret that not even the Brotherhood knows why it's called like that.   Danger lurks around every corner. Crowds of fanatics aren't the only obstacles you need to overcome on your journey; traps and environmental elements also pose a grave threat. Watch out, since just 1 wrong step is all it takes for the laser barrier to slice you into 8 pieces.   This journey will be long. Challenging. And exciting. You will face 24 huge and complex levels across 6 acts. Escape the prison by sneaking through a secret laboratory, sand dunes, and an ancient castle that holds thousands of years of Brotherhood history. No one is with you. All you have is yourself. Your shotgun. Hordes of enemies. Animal rage and the desire to kill. Destroy Them All!