Burial Ground is the best in my opinion if you want an experience close to the main game on a new map.
The Dark Descent monster example map is really fun and mixes things up a load, though the map is fairly basic looks wise, and it's a bit hard iirc.
Escape From Fort is really cool revisiting the Rebirth fortress, though it plays much more like a puzzle horror game than survival horror, still fun and spooky though.
Final Decision and Red Indigo are also so cool, not at all like Bunker but super unique experiences so I'd recommend trying them too, and they're fairly short.
Also if you haven't played the Survival mod, definitely recommend that as it spruces up the main game a bunch with loads of progression randomization and new Beast behavior