Heavy Bolter: Very good for what it is. Perhaps the wind up time on full auto is a little slow, and setup/teardown times for full auto are fast.
Plasma Cannon: I don't know where to begin with this, so I'll just try; the mortar-barrage ability is super-weak and should be boosted considering its cooldown. The single-shot charge with CD ability does little to justify using it. The rapid fire form just overheats to fast and does nothing to justify using it in any situation. The most basic single shot fire mode (left click) is usable, but avoidable as it provides little beyond killing warp gates.
Power Sword: Very very very very very weak. The cleaving-cone attack CD is too large. The single target attack is too weak for the amount of danger it puts you in.
Power Axe: See Power Sword. Side note; it does do very nice damage against terminators considering its flaws.
Power Hammer: I used it twice in combat and switched immediately after I realized both times that I couldn't find a way to not take 50% hp damage in a few seconds with it. It needs a better engage rather than relying on having the jump pack, which is mega-unreliable.
Chain Sword: See Power Sword. Side note; I like using this against unarmored foes as it handles them well enough considering its flaws.
Plasma Pistol: See Plasma Cannon. It doesn't have anything that justifies taking it in your loadout.
Bolt Pistol: Shoots well, has a great close-range damage buff, and is versatile. Love it. Would take it over the jump pack for ranged engagements any day.
Autopistol: Probably the only pistol I'll ever use again other than the bolt pistol. Works well with a melee build and provides the much-needed ranged engagement methods.
Boltgun: Good for what it is. Could use some knockback/stagger to go along with the concussiveness that boltguns should deliver.
Plasma Gun: See Plasma Cannon. Needs more oomph. It feels like I'm spitting rather than creating miniature stars.
Shotgun: Perfect. Devs do not touch. Players need to have this in their off-slot.
Flamer: Hilarious to use against nurglings. That said, I think the cone on all of it's attack forms needs to be widened just slightly.
Meltagun: Very fun to use, does what it sells. Well balanced except that it could use some DoT damage on other attack forms and some extra damage to structures.