The Flamethrower emits small cylindrical bricks, that tend to pile up in front of the user, acting a a sort of shield for a moment. If you are close enough, or attacking from above, you can score an easy kill. Although each small block does very little damage, a flurry comes out when you fire it, with a small amount of spread, so you can easily hit targets from afar.
It does no damage to buildings or loose blocks, just to players. The Flamethrower can intercept missiles, super balls and slingshot balls, useful as a defensive weapon, as well as an offensive one. With it's relatively low (~3 seconds) reload time, it makes a great weapon to always carry around.