I think a cool way to make javelin unique would be to give them Valkyrie rockets, so when fired, the player takes control of the rocket and steers it with the mouse. Give it a 5 sec fuse or exploding in impact / with right mouse button, and make it do 170 dmg on direct hit and 110 splash with extreme fall off.
The sights could be a little screen with the rockets view, and you have to aim before you fire. Give the rocket a speed of 430 or so, and 50 hp and then people can shoot it down, giving them a counter play. Cool down could be around 30 secs.