The game is an absurdist parody of Konami's Metal Gear franchise, using fourth wall metahumor, running gags, and action film tropes throughout its presentation and gameplay; the game's protagonist, Jesse Fox, is a direct parody of recurring Metal Gear protagonists Solid Snake and Naked Snake.

Some level segments feature unique gameplay, such as a shoot 'em up-esque boat battle with an attack helicopter or a submersible section reminiscent of Metal Slug 3.

While searching for a way out, Fox learns of "Operation Jerico", a large-scale attack plan by the X Army, and meets and falls in love with the Doctor, the sole physician of the base's sick bay, who rejects his advances but agrees not to turn him in.

The pair approach a security checkpoint, but the soldier checking their passports recognizes Fox and lets them pass, impressing his previously skeptical girlfriend enough for her to kiss him.

In a post-credits scene, the soldier from the checkpoint reveals to a colleague that Fox simply bribed him to "recognize" his heroics, and that the entire story was made up "just to score".

[10] The game's player character, Jesse Fox, was originally created in 2018 for Afraid Project, a strategy game that donated money to African humanitarian aid NGOs based on the player's progress,[12] in which Fox was an aid delivery driver;[11] however, Afraid Project was canceled when its Kickstarter campaign failed.

[13] The game was among the indie titles that were teased in the Guerrilla Collective showcase at E3 2021, the final Electronic Entertainment Expo before the event's retirement in 2023.

[18] In a review for PC Gamer, Joseph Knoop praised the game's humor, the influence of the unreliable narration, and how it captured "Hideo Kojima's flair for bonkers storytelling, villainous monologuing, and action hero logic".

[2] Francis DiPersio of Hey Poor Player similarly lauded the humor and influence of the narration on gameplay, saying "there were moments that literally left me in tears and gasping for breath as if I were infected with FOXDIE", though he also criticized the "obnoxious" difficulty of two maze segments that must be completed without errors.

[1] Daniel Weissenberger of Gamecritics.com called UnMetal "one of the most successful comedy games of all time" and commended how well it parodied Metal Gear and Kojima's "ultra-serious" storytelling.

Maciejewski of Video Chums found the game funny and highlighted the viability of non-lethal weapons, but criticized the trial and error nature of certain segments and boss battles that force the player to lose repeatedly to learn how to proceed.

[6] Arana Judith of WellPlayed liked the game's concept of lampooning Kojima's works and complimented the strength of the gameplay, but she disliked how the player is forced to heal enemies they shoot, calling it "tedious" especially after the alarm is triggered, and described the cover system as being poorly-conveyed and too limited to effectively hide with.