Yeah, long-range, it's often somewhat useless for me. Enemies move too much. Close-range, however, it's a real treat, and probably the best thing for Elites. I use it as my primary weapon for every single level, with my secondary weapon alternating between Pistol (Pillar of Autumn, Halo, Silent Cartographer, Assault on the Control Room), Sniper Rifle (later half of Halo, Truth & Reconciliation, maybe a teeny bit on Keyes), Rocket Launcher (very end of Silent Cartographer, specific parts of Assault on the Control Room or Two Betrayals), Shotgun (343 Guilty Spark, The Library, Two Betrayals, Keyes, The Maw). Yet I always have that little Plasma Pistol by my side, no matter what. In the right hands, it is truly devastating.

Vale,
Perseus