I feel like I'm missing something with this skill. Dart-Splinters can do 180 dmg for 10 mana while Spirit Barrage does 190 dmg for 108 mana. Okay, so it can target in the back, that's nice I suppose (though surely not worth 10 times the cost) but so can Haunt which, runed, can do 288 dmg for 98 mana and can jump to multiple enemies. It just seems so much less efficient than either of these as a single-target skill. Even with the +mana rune it doesn't seem worth it over Dart or Haunt. (Haven't gotten to the other runes yet but they all sound lame.) Am I missing something?
I use Spirit Barrage as my main left click attack. It does a lot of damage, casts quickly, and hits more reliably than any other skill.
With mana regen gear, blood ritual, rush of essence, and the mana refund rune, Spirit Barrage actually gives me mana back when I cast it. I think it's a good skill...you just need a proper build for it.
Haunt only gives a set amount of life, which means it doesn't scale with damage. Also, Haunt does 280% weapon damage over 2 seconds, and doesn't stack with itself. Spirit barrage can hit for that much every single cast...you can cast it a lot more than just once every 2 seconds.