The Rocket Launcher increases Marine's grenades count from 3 to 15. The same somehow applies to Noir Lime too. If you pick it up during a level, you'll have to finish the level before getting the grenade bonus; if you buy it, you'll get +12 grenades instantly.
The rockets will begin to fly in circles after traveling a certain distance, making this gun less effective at long range.
If you fire it right under yourself while ducking, the rocket will not explode immediately, and will bounce off the wall instead, possibly flying away.
The rocket can bounce off walls at a certain angle, unlike its Plazma Burst 2 counterpart.
If it flies for too long, in disappears without any explosions, unlike Plazma Burst 2 explosives.
It is the only weapon in both games that has limited ammo, not counting grenades.
The Rocket Launcher will not be added to Plazma Burst 2, however it will be added to Plazma Burst 2.5.