The Justicar soul is more of a front-line survivor with some heals to boot. If you want to DPS you can either go for a soultree designed for that, or supplement the justicar soultree with another. I brought up a lvl 23 Justicar/Druid by the end of Beta#7 and was really enjoying the build.
I didn't get much group time in, but there are some heal single-cast spells that are handy. The justicars primary heals come from a percentage of damage done to your enemy, and is an AOE. There are places in the level progression where mana-starvation can start setting in, but there are mana generation techniques that you can build to. Whithin the Druid tree is the Fae hammer, and that was always good for bring the mana back up. Having a multi-enemy melee strike is handy as each enemy hit will bring up the health-bar. That Fae hammer only works once per swing on the mana regardless of the number of enemies hit.
My third soul was for the lack of knowing much of anything about the souls, and it was a shaman. There's some good hard hitting stuff on that tree. Do some shopping, but I suggest that you try a Justicar if you like to step into the fray.