I had a great time with Unbound. I also enjoyed playing Eternal X which made Gen 6 actually tolerable to play, although it’s largely the same game as Vanilla X with all Pokemon through Gen 6 catchable and improved difficulty.
Pokemon Emerald Rogue. It's a Pokemon Roguelite that includes most (all?) Pokemon and mechanics from every game. It is very challenging, but it has tons of customization options. It has a lot of modernization and quality of life changes. It is basically perfection in my opinion
I haven't really played any romhacks besides one. A while ago I played through the Gold Quest for Ocarina of Time. It's like an upgraded version of Master Quest: remixed dungeons, enemies added in different locations, items have been moved to different locations, and some changes to the world outside of dungeons. Great for anyone that wants a more challenging version of OOT.
I've also been watching a friend play through a Pikmin romhack called Bikmin 269. This game is straddling the line between a shitpost and a fever dream. You collect NFTs and Bitcoins, the ground texture is layered images of Shaggy from Scooby Doo, the space ship is a T-posing Luigi, and one type of Pikmin is a "mushroom" that looks suspiciously penis-like... It's a nightmare in the best possible way
The Secret of Evermore hack enabling a second player to control the dog is quite formidable, if a tad glitchy at times. It elevates a somewhat forgettable single player jRPG to a fun co-op pastime.
There was a genesis version of shadow run where they fixed the bug with melee and to much cyberware and allowed you to choose your race at character creation. They have not been kept up though it did not really work for me in a recent iteration.