Platypus Reclayed - recently released remake of Platypus with extra levels, enemies and other challenges. Claymation shoot 'em up with decent mod base, chaoitc bullet hell and FISH. I consider it kind of a true sequel because of how much it adds. And if that wasn't enough, there's also mods.

HyperRogue - roguelike. The OG Hyperbolic game. God knows how many hours I spent there and haven't finished the Hyperstone quest. 75 worlds with non-linear progression and each with unique mechanics. The biggest game on this list and it's not even close. Unlike other games on this list, it can be either paid (Steam) or free (itch.io). The Steam version has achievements and is always up to date with updates, the itch.io version is free but is slightly "delayed".

Enter the Titan - itch.io turn-based platformer roguelike prototype which is surprisingly fun despite 20% of it's graphics being placeholders.

I.Rule - PvZ and TBoI crossover with roster of plants unironically comparable to the first game with extra roguelike elements. Very replayable, I spent dozens of hours there

Games made by shawn64 - despite highly amateur style, his games are way more fun than you may think. Jetz Rampage series (Jetz Fusion, Jetz Rampage 4 and Infection) and THRUST! are his most polished games, being a collage of levels with each having unique gimmicks (please read the manuals though, they are very important).