Jupiter Hell is obviously a labor of love by someone who understand roguelike play. At its core, it is a fairly simple run-and-gun roguelike but there is a decent amount of depth to it. The main engagement is shooting from cover and drawing enemies to cover that benefits you but not them, so each room is typically approached by blasting a door from a distance or retreating to cover on enemy sight and doing a little dance in cover to draw the enemies out while trying to make sure you aren't getting flanked. Lethality is incredibly high for both you and the enemies, most enemies drop in one hit if you are playing smart, but securing that hit relies on the cover game mixed with your loot game, both luck and planning portions.
Your inventory is limited, there are almost no consumables to escape from trouble and most slots are devoted to health packs and ammo. At the same time, over the course of the game you will be going up tiers of weapons and ammo, but upgrades aren't so scarce; you CAN use them on starter guns and good starter guns can be carried beyond their worlds if properly cared for. There is a wide variety of guns, rifles, shotguns, handguns, launchers, including some rare and unique variants, but you can only pack a small number, typically 3 of them, so you have to pick carefully.
There is a lot of good quality of life stuff here: The game has a very fast pace, even though it certainly doesn't clear quickly. Despite the 3-4 hour run time (That's some ♥♥♥♥♥♥♥ coffee break!), you are constantly moving from room to room, constantly cover dancing and blasting baddies. No time is wasted on tedious garbage like unloading guns or stupid item relays or other sorts of dumb roguelike crap. Most of the early levels offer extra instant healing above the bare minimum to ensure that even a bad opening can make a comeback with lucky play. The scaling is balanced decently well, keeping the game tough throughout without turning into a drawn out early slog or a late game cakewalk like certain other roguelikes. The game offers several extra challenge modes too that shut off or overtune various game mechanics to shake up your play, and also a wide array of difficulty options that are balanced to allow the game to pull punches without feeling patronizing. Leveling just gives you a perk point to select from a small but varied list of perks that all meaningfully shake the game up. There are a couple mandatory picks and while there are several specialties, most of the generalist options tend to be stronger even with the ideal specialty gear. Each class has their own set of perks and special abilities too. Plus, the game continues development even today, even outside of early access, showing the typical roguelike dev love.
That said, there is absolutely no protection against double-moving upon seeing an enemy (Unless you are holding the arrow keys which nobody who plays roguelikes does.) or any warning about how close you are to death or how close your armor is to breaking. The devs don't want to put stops in the game to impact the pacing, but I am not sure the devs couldn't learn from Cogmind on this. In addition, despite the devs not wanting you needing to use wiki spoilers (Again, they don't want you wasting your life with trash roguelike time wasting), the Archmedusa's unique attack mechanics and the characteristics/challenge/loot/enemy makeup of 18 ♥♥♥♥♥♥♥ different branches through the game ABSOLUTELY DEMAND wiki knowledge.
But as for why am I rating it negative? Because the cover game is really all there is to the whole experience. There is a lot of depth and nuance to it, but if you see a bunch of insane hellbeasts in a hallway, there is no game you CAN play. There are a few melee-focused builds that CAN in certain circumstances handle situations like that but those are the exceptions. Lethality is so high and damage you take snowballs so fast that one bad hallway can end the game easily without any counterplay. Despite the game being paced so quickly, you can still lose a couple hours of a run to that nonsense and it stays endlessly infuriating.