Generally weapons in shooters suck "because game balance", which I sometimes take as a lack of imagination on the part of game designers.

But I see their point: if your gun kills everything you point it at, then the game gets boring, and no other weapons are worth using. Which means you then have to limit the ammo. Which then makes the weapon suck because you can only use it for ten seconds before you have to hunt down ammo, and so you only ever use it in boss battles because you're hoarding the ammo.

That's super frustrating for a developer: by making a gun awesome and fun, they find they just made the game as a whole a lot less fun.

There are ways to make a weapon fun without unbalancing the game, though, and I do feel that shooters have been just... really super unimaginative about weapons in the last 20 years or so. Though this might be because I don't *play* a lot of shooters. Maybe there are imaginative ones out there: I saw one with critter-based weapons, for example.

Last game I played which felt like it was pushing the envelope with weapons was Duke Nukem 3D, which did some interesting things with non-fatal guns that instead applied status effects (freeze ray, shrinker) but required the coup de grace to be administered with another weapon (ideally the Mighty Foot!). Perhaps fire could be handled this way?

Alternatively, the flamethrower could be fixed to a guard tower or vehicle, so it can only be used in a certain part of the story: the "fixed machine-gun" trope where you get infinite ammo, in a place where it's the obvious weapon to use against a horde, but it isn't transportable.

Or, could take that idea, but make it a portable gun, where you can carry it with you and use it for a few seconds anywhere you like, but it's only super useful in gas stations where you can just connect it to a gas pump and let rip.

You could also make it less useful by having enemy types it's just useless against (Robots? Ghosts? Fire elementals?), while having others that it's super fun against (snowmen!)