The Plasma Rifle could be a nice weapon, but his range is much too low.
All weapons used in pvp have a better range (Avenger, M60, Rocket, Sniper, Gauss, Gatling and Laser Rifle), so if we could compare it directly you should take 2 bursts in your face before making one of your über-powerful-plasma rifle critical.
Though I think this weapon is good versus mobs or for killing some random bluesuits.