Currently i wanna say Enter the gungeon, i love the game it is alot of fun to play, great music aswell which is a bonus, but the game is fucking unforgiving as buggery.
For those not familiar it is basicly a top down dungeon crawler with bullet hell mechanics and a huge selection of guns and items, random levels and different characters to play as (they all play fundamentally the same but start with different kit).
Essentialy the only way to win is to not take damage, which might seem straight forward but in practice is pretty tough, the game basicly has a better play = better rewards system, that includes healing items, armor, ammo, money, chests which can contain anything from a certain pool and keys to open said chests and certain doors with. The more rooms you clear without recieving damage the higher chance somthing will appear at the end of a room, get hurt too mucn and lose out on pretty much any chance of a win.
Unless you can consistantly kill boss's you will pretty much never unlock any new stuff, as much of it must be purchased with ingame currency that only appears after boss fights, many of the items on sale are usefull upgrades that can make or break a run.
If your thinking this sounds a little like binding of isaac, the comparison is realy only surface level, it is far more hectic and requiring skill rather than over powered item combos to win. There is no super combo, just simple good items and passives that can stack.
To sum it up, enemies all over the place, some of which explode or ignite the floor on fire, projectiles coming in from all directions, enviromental hazzards, and to deal with it you have to stick it out with the rather lack luster starting gun until you can earn a key to open a box which might give you a better one, which is nice until it runs out of ammunition.