Diablo 3 works a bit like a snowball: you start off having to really watch yourself when you encounter an elite enemy, and your abilities are a mix of what seems cool at the time. However, once you get to level 70 and hope and pray to Rathma (or whomever) for set pieces, and those prayers start getting answered, things get kicked into high gear.
At this point, I have full sets of Trag'oul and Inarius armor for my Necromancer, and I'm close to complete on the Rathma set, and the Plaguebringer set I actually have six pieces, but need to farm Death's Breath in order to transform pieces until I get all six individual parts.
While I'd like to get a Rathma-based set going, I haven't quite figured out the survival game for that playstyle (using Icy Veins as my guide - I don't like that their build doesn't use Army of the Dead, which, unless I'm missing some Legendary that causes it to go off automatically, seems like you wouldn't want to bother with a six-piece bonus.)
The easiest one I've been able to work with is an Inarius build that uses Corpse Lance and of course, based on the set, Bone Armor. The Inarius set greatly increases the damage done by Bone Armor's activation, and also ups the defensive bonus from the set as well. At 6 pieces, it causes the bones to whirl around you, dealing a fair amount of damage to anyone nearby and I think just generally buffing your damage.
The build is very bursty - using Land of the Dead to fuel Corpse Lance and of course waiting for Bone Armor's cooldown, you'll utterly annihilate rares and elites if you can burn your cooldowns, but until then you're just going to be running through with your swirling bones and Grim Scythe-ing enemies. This is a close-quarters build.
Trag'oul also uses Corpse Lance, but this is a build that has absurd damage potential and can very easily kill you even if you aren't getting hit, as it's all about your life-spending abilities. Still, if played with finesse, it has a ton of potential, but the funny thing is that you will definitely be using Blood Rush all the time to give you a corpse to start the process going.
While leveling up I used lots of minions and Corpse Explosion as a major source of damage, and I'd like to find a build that incorporates those elements, but for now I'm very much still farming non-set pieces.