If you've ever played The Binding of Isaac or Enter The Gungeon, then Monolith is immediately familiar stuff. A comforting blend of twin-stick shooter and dungeon-crawl wherein you navigate mazes, hoard loot, upgrade your character (cute little spaceship-people in Pop n' Twinbee fashion), fight menacing-looking bosses, and then do it all again with even more stuff unlocked in the dungeon generator. What sets Monolith apart from its peers, and what has earned it a near-perfect user review score on Steam, is just how little all of that progression means.
Weapons are ammo-limited and ephemeral, upgrades tend not to be especially dramatic, and progression is rewarded by an ever-increasing difficulty level. In Monolith, the most important weapon you'll ever use is the starting pea-shooter. Your default, unlimited-ammo machine-gun may not spit out quite as much damage as the fancier weapons, but it'll still do the job if you're able to dodge bullets for just a couple seconds longer. There is nothing in Monolith that you cannot defeat with raw reflexes and knowledge of enemy patterns alone, and knowing that makes every victory sweeter, and every defeat sting just that little bit more.
The focus on raw skill and bullet-evasion only increases over time, contrary to the creeping chaos of Isaac's expanding and increasingly unhinged dungeons. While you may unlock a steady stream of new weapons to find and use over multiple playthroughs, they tend to be geared towards individual styles of play, rather than being objectively better or worse, and their ammo-limited nature means that there's always a chance you'll run dry at a critical moment anyway.
Powerups, while useful in Monolith, are not the means by which you'll master the game. They're a safety margin; a buffer between you and the swarms of bullets, designed to mitigate the inevitable human errors that you will make, and that will hurt so very badly. Extra health and screen-clearing smartbombs will let you push forward just that little bit further at the expense of your final completion score, but when push comes to shove all that matters is how good you are at not getting shot.
The ultimate culmination of this trend within the game is Hard Mode. An extended, more challenging dungeon unlocked after completion of the base game with new boss attack phases, more aggressive enemies, and a True Final Boss that should be experienced first-hand, not spoiled. Without giving too much away, I will say that when you go into the last fight of the game Monolith visibly sheds the last of its dungeon-crawling pretense, plunging the player into a battle worthy of any Dodonpachi's final act.
Monolith is available for £5.59/$8 on Steam, and comes with my highest recommendation.