Just played through the campaign with the mod and had a great time!

However, to me, the Flamethrower feels quite underpowered for how rare it is, and due to it's slow projectile speed, and poor visibility while firing, it can be rather ineffective in combat.
Another issue, is that it has worse crowd-control capabilities than one would expect. Often, I'll shoot a burst of flames into a tightly grouped cluster of enemies, only to find that it effected one single target. Sometimes, I try to shoot something right in front of me, to no effect.
I feel that these issues may be due to the large projectile size causing projectiles to get stuck on walls, floors, and single enemies.

Suggested fixes:
* Make projectiles pass through enemies
* make projectiles bounce off walls (only at obtuse angles to prevent self-damage)
* give projectiles a smaller collision hitbox, while keeping a larger hitbox for dealing damage.
* Increase the projectile speed a bit

I'm not a modder, so I'm not sure how many of my suggestions are feasible, but I hope my feedback was helpful.