No revenue estimate for GOG — its rating/review counts don't calibrate to sales the way Steam's do. The Steam version is estimated at $714K — a different platform, not this one.

The Citadel

Go forth, Martyr; For you are the finest among the Battlesisters; Go forth, and LET THE SLEEPING GOD DIE Descent into the depth of The Citadel THE CITADEL is a hardcore, brutal old-school shooter full of action that's a throwback to the 90's classics that we all love. Fight through 6 Episodes of 30 action packed levels (and an additional 6 secret levels). Face off against 6 fearsome bosses. Carry 14 different types of weapons, with obliterating secondary fire functions. Make the world tremble with 3 types of single-use special weapons. ・Unlimited Continues. ・You can continue trying until you break. Hub areas serve as respite if you find the episode to be too difficult. ・Completely skill based: no cheap Hitscanner, all projectiles. You live as good as you dodge. ・Huge enemy variety and diversity. From axe throwing cultists, to suicide drones, to mecha tanks, and flamethrower troopers. Kick the Opponent into Lava! ・Light-weight enemies can be kicked and stunned. Get your positioning right, and you can also make them fall into a bottomless pit or lava. Upgradable Weapons ・Some weapons can be upgraded or switched to superior versions. Gibs! ・Enemies explode into chunks of meat or metals when they die. Ouch! Optional Features: Leaning and Weapon Jam The Citadel contains numerous optional features for added replayability and difficulty. ・Leaning can be enabled in a option menu. Dodging is not the only way to avoid the enemy fire. ・Weapon condition features can be enabled in a option menu. ・Automatic weapons can be jammed in the middle of a battle, and they will be eventually broken.