I love shotguns so much it's unreal.
Need to hit something big? Buckshot.
Something small? Birdshot.
Wish you had a rifle? Slugs of all kinds.
Need something on fire? Dragonsbreath.
Wanna fuck up the guy behind a door? Breaching rounds.
Wanna fuck up the guy behind a door, but you don't actually want to go inside? Ferret rounds.
Want to try to avoid killing the guy? Rubber pellets and beanbags.
Need to shoot a flare? You can do that too.
Want to put a bunch of tiny darts in something? Flechette.
You can stuff whatever you want in a shotgun shell and it'll probably work. No fancy sights needed, just a brass bead.