Thrill Kill is an interesting example of this. The game was basically finished, but received an Adults Only rating, and then wasn't released. The devs supposedly leaked a copy of it, and it became one of the most widely pirated PS1 games.
The engine was later used the in the Wu Tang Clan fighting game Wu-Tang: Shaolin Style, some X-Men Games and Rock Em Rock Em Robots game so it wasn't all bad.
Agreed on it being fairly decent too, but nothing to write home about (sans the violence).
https://en.wikipedia.org/wiki/Thrill_Kill
Played a lot of it in college. Fairly decent four player fighter.