So, I played the Engineer to 12 and the Sorc (Destruction side) to 18. Here is the Engineer Skinny:

Leveled fast. Although the turrent's don't move, they are pretty hardy. They are great in PvP as you can plop one down in the middle of battle and back off to snipe. In fact, in PvP my Engineer causes all sorts of problems for the opposing faction.

I try not to let anyone get close to me so if someone approaches, I run. But, my gun stays put nailing my enemies until I can regroup.

There are some nice interrupts. Timed with a dot, a direct damage and an interrupt, a shaman is made short work of.

The only reason I didn't level my Engineer farther is I deleted my book (like a recall stone in WoW) and I have yet to find a way to replace it. So he is stuck in the far reaches of a map :)