Tempest is actually fairly complex. I have three different rotations to swap between, and positioning is more important in Tempest than any other spec. Setting up, DoT timing, gauging an enemy's remaining HP and knowing a fight is also more important in Tempest than many other specs.
Overall, Tempest has two or three things going for it that makes it shine in current content - the highest burst over 15-20 seconds in the game, great setup/ability to make use of downtime, and strong passive cleave. The ST damage is not actually over the top. It's just that with boss phases lasting half a minute and adds everywhere, Tempests get their wavelength up for every boss phase and can cleave like crazy.
I've said his before and I'll say it again. Clerics are the only calling that aren't competitive in ST DPS at the moment. Rogues have assassin, BD (both of which will scale like crazy with high tier eternals) and to a lesser extent, Shadeborn. Mages have harbinger and (I think?) Pyro, as well as the best possible support. Primalists have their wonky specs (which also have good cleave and can make really good use of their eternals).