My experience with it is that it is actually very good vs elites. (Elites that use vortex, wall will give you some problems as they can interrupt channelling). People complain about the fact that you are standing still. Basically, if you have mortal enemy on the elite, and snap shot gloom you can channel forever. As long as you have some tanky stats, the non stop life steal keeps you going even when standing in moltens. *Please note that I use a Manticore (slower attack speed), easier to keep going.
It will be a cool ability in 1.08. I think there are 4 runes that are pretty balanced:
Bombardment: I really don't like the way that these little bombs travel. Unless you have someone tanking for you, I find that this misses the target all the time especially for fast elites.
Fire Support: Clearly the best rune for single damage. Use with spit fire turret. An issue I find is that its very easy to run out of hatred, if you are trying to ensure turrets stay up and use rapid fire.
High velocity: Somewhere between the 2 above. Better than bombardment for single target, more AOE than fire support. A not so obvious benefit here is that if you have an elite marked with mortal enemy and minions come between you (this happens all the time), you can still fire in the direction of the marked elite and the pierce can still help you generate some hatred.
Withering Fire: Most popular RF rune right now on diablo progress. For good reason too, the reduced cost of starting is useful in terms of practical play (especially solo) i.e. when you come across vortex mobs etc. your attack will be very much start/stop. I think with a Manticore (slower attk speed) and the bat and other hatred regen, this rune can be effective without mortal enemy.