Flamethrower
As the name implies, the flamethrower sprays a jet of incendiary liquid at its target, causing immense damage to anything caught in the blast. The flamethrower completely ignores cover when calculating damage to its victims and is capable of hitting multiple units with a single shot. This makes it invaluable when clearing fortified positions or ambushing enemy units, where a single flamethrower can turn the tide of the battle in seconds.
Unfortunately, the flamethrower also has some major drawbacks, not least being the fact that the user has to carry pressurised containers of highly-flammable liquid around with them. Flamethrowers also damage indiscriminately, destroying items that could otherwise be recovered. It is also highly dangerous if used carelessly, as the user can easily accidentally douse a comrade (or themselves) in napalm when firing the weapon in an enclosed space.
Ballistic Machinegun
The machinegun is a supremely effective anti-personnel weapon that fires long bursts, causes serious damage to infantry and is capable of punching through extraterrestrial armour with little trouble. However, as a heavy weapon, it suffers a number of inherent limitations. A considerable amount of time is required to shoot or reload the weapon, it is inaccurate when not fired by a stationary user, plus the weight and recoil of the weapon necessitates a strong trooper carry it into battle.
As with all heavy weapons, the machinegun is devastating when used correctly but leaves the soldier operating it vulnerable to enemy attack. The sheer weight of the weapon and the ammunition means that the gunner can only wear light armour into battle, and the significant accuracy penalty for moving in the same turn that the weapon is fired means that it is vulnerable to flanking. Despite this, the fearsome firepower of the machinegun means it is still a remarkably powerful battlefield tool.