I chose necro for my main and I am currently at level 25. I would say that it is a very hard profession to kill despite the light armor. I have succesfully tried three different builds so far:
1) Minion Master (up to 6 permanent minions at your service): I didn't like this one because you have to continuosly cast minions (they die all the time) and that's a bit annoying. Minions die often because they don't heal out of combat and because they are very "sensitive" to strong AoE attacks. However, this build doesn't seem to require high movility, and makes you quite tough, so it's probably a good choice to get started.
2) Condition Necromancer: Instead of relying on your minions, you rely on conditions (and boon-steals) to defeat your foes. Very fun to play imo, both in PvE and PvP. Probably the most fragile of all three builds (but still quite tough).
3) Melee/Death Shroud (dual wield daggers): You lose range in order to get life-steals and higher life force generation, which allows you to spend more time in DS form. This DS form is improved by means of traits (better skills and so on).
I will update this post as soon as I get more experience.
Starting up the Necromancer Awsomesauce thread. Been playing for a while, sitting at level 32. From what I have gathered, it's a condition inducer, boon stealer, and undead summoning being of destruction. In addition to the regular form, every kill gives you a green orb that builds your life force meter. Shifting form grants you four new abilities, one of which is a very awsome AoE life steal. Attacks done to you while in this form reduce the life force meter. Once you shift back, your life is exactly where you left it. If you kite the target well enough, the CD on your healing ability will either be almost done or already done, allowing you to heal if needed.
Personally, I love my staff build that creates deadzones out the yin yang, while tossing in Poison Cloud, Well of Suffering, and Well of Corruption. In PVP situations I use Marks to create traps for players, while using the Clouds and Wells in situations where everyone is fighting in an area and paying no attention to me.