Just discovered that player blogs exist and decided to write down what I learned playing this character!

General Facts:
1) Once you understand the basics of the game, Nightmare seems much easier than Normal. Turns out, most rare creatures are really easy and getting lots of their drops is really good. At the very least they sell for decent chunks of gold.

2) Adept is ridiculously good for classes that have a lot of point demands like Necromancer. I won't say it's broken because there are other ubers that can be crazy good like that, but it's definitely a solid pick for Necromancer.

3) Conversely, I'm not sold on the Lich transformation. Obviously going Cornac -> Lich is strong, but there are some racial trees out there that I think are really good and in retrospect I was really wishing I had picked up Master of Disasters. Necromancers have so many baked-in and easily obtainable Spellpower bonuses that you are constantly spellshocking everything, and Corruption/Curses can ensure you're doing it very consistently.

4) Necromancers don't require much Willpower. Their spells and sustains are generally cheap on Mana and they have very powerful mana regen options. Also, no amount of Willpower in the world is really going to save you from a Mana Clash, but Consume Soul will. Even if you pick up Corruption/Curses like I did (and I heartily recommend), save the curses for challenging rares and bosses and you will have more than enough Vim.

About Necromancer Trees:
Spell/Glacial Waste -- Hiemal Shield should not be used the usual way. Instinctively you see that it's a sustain and go "Alright, so I turn this on and leave it on..." No. Necromancers are going to have a relatively high DieAt stat, and Hiemal Shield should be preserved until and flicked on when you are near death to get the maximum power out of it. If used in this manner, it would be pretty trivial to get something on the order of an effective 1k, self-healing damage shield. The retaliation damage Hiemal Shield does is very trivial and having 100% uptime on it is much less valuable than having the full-power shield effect on you when you're sub-1 HP. I went 4/2/1/4 with Adept last time, next time I'm leaning more towards 3/1/1/3 with Adept with the 1st, 2nd, and 4th skills being options for luxury points. Without Adept I think it's pretty much a hard 5/1/1/5.

Spell/Nightfall -- Invoke Darkness and River of Souls are the Necromancer's bread-and-butter of blowing stuff up, and while Night Sphere is a nice crowd control spell, it doesn't scale well with talent points IMO. I went 4/1/1/4 with Adept, next time I'm thinking 3/1/1/3 here, too. Without Adept you're definitely going to want 4-5/1/1/4-5 and might also want to bump Night Sphere's radius with a luxury point or two.

Spell/Age of Dusk -- I think on Nightmare this tree is a trap. It does all kinds of cool things, but the fact of the matter is that all those cool things it's doing rely on Dire Plague being active and ticking on a crowd of enemies. That's just not going to happen in Nightmare. In Nightmare you're going to cast Dire Plague, everything around you will die in 1-3 turns, and then all your investment in this tree will essentially give you random Invulnerability turns but otherwise be useless for some 20 turns until Dire Plague comes back off cooldown. I went with 5/3/3/3 with Adept last time, but I'm not going to unlock it next time. If you really want to play with this in a low difficulty, do 1/3-4/3-4/2-3 with Adept. Without Adept, add an extra point into Dire Plague just to make the soul rip chance higher than 1%.

Spell/Grave -- I saw this as a minion support tree and didn't really get into it. In retrospect, this tree deserves some investment even if you're not working with minions. The first two spells, Black Ice and Chill of the Tomb, are decent bread-and-butter combat spells in their own right with the minion support added on. The third spell, Corpselight, is... interesting. I'm not sure I'm sold on it, but it could be a good setup for a big crowd control combo in a dense room of enemies. Next time I run Necromancer I'm thinking of going with 3/3/1-3/1 in this tree with Adept.

Spell/Death -- This is the tree that led me to pick up Corruption/Curses. Rigor Mortis is a solid single-target nuke on a heavily debuffed target, easily critting for at least 1k damage as early as level 25. Utterly Destroyed is also an amazing one-point-wonder with Adept. Grim Shadow is a talent I really want to like, but honestly the radius is kind of weak, making it kind of a generic buff. Maybe it gets more value in higher difficulties. I went 4/1/4/1 with adept. Next time I'm not putting 4 points in Grim Shadow unless it's absolute luxury points -- I'm thinking 2 but maybe it's fine with 1.

Spell/Animus -- Sort of the engine that powers the Necromancer. Soul Leech is going to be your primary method of gaining your special resource -- souls. Torture Souls does a great job clearing levels with Spikes of Decrepitude, and Consume Soul and Reaping are just skills that make you better at doing what you're going to do. I went with 3/3/3/3 here with Adept, but I'm thinking more along the lines of 2/3/3/2 next time. Reaping definitely doesn't need more than 2 points with Adept, and Soul Leech is more about what you find you need. Maybe I'll put 1 or 2 more points into Soul Leech when I actually play.

Spell/Rime Wraith -- Maybe I wasn't playing it right, but Rime Wraith just doesn't flow with the rest of the class the way I was hoping. Maybe if you have minions it's better since the Wraith will fly around healing them, converting their damage, etc, but I think it just kinda sucks. This is the cat point I'm going to pocket and save in order to not go Cornac next time.

Spell/Dread -- These things seem like excellent support minions, and if you take Adept there's really no excuse to not throw at least 1's across the board here. Luxury points probably go to Soul Eater, but boosting the first or last skill for extra talent levels is also valid.

Other Class Trees -- I haven't played around with them, yet. My strategy for this playthrough was to do a solo Necromancer kind of play, but that really doesn't seem to be how the class is designed to work these days. Now it's all about the synergy between the Necromancer's blasting spells and the minions, and there are a lot of spells out there that buff minions. I will say, however, that the Ghouls will Retch and that Retch will heal undead, which is why my next start will definitely be a Skeleton (also, I finally unlocked Skeleton after killing that stupid Master way too many times and getting RNG screwed). My plans are to go for 3-4/1/4/0 in Spell/Master of Bones, 3-4/0/0/0 in Master of Flesh, and 3-5/1/1/1-3 in Master Necromancer.

About Generic Trees:
Combat Training and Staff Combat -- I went 5/1/1/0/0/0 in Combat Training and 1/1/1/1 in Staff Combat. This gives a nice blend of defenses and armor as well as a spammable spell that I can throw when everything else is on cooldown (happens a lot if you don't invest in both Grave and Nightfall). I'm probably going to stick with this because I'm probably going to wind up with a silly number of Generic talent points and even the last Staff Combat talent isn't bad when it's level 2.5-2.8 for free and you're throwing around Curse of Defenselessness.

Spell/Spectre -- I went 1/1/1/1 here and loved it. I can see myself eventually throwing more points into this tree, but this baseline investment is just really good. Ghost Walk is premium mobility, Spectral Sight and Intangibility enhance it very nicely, and Path to Beyond gives it an extra playline. I'd probably throw some more points into Ghost Walk but I don't know.

Spell/Necrosis -- This is the tree that actually drew me to playing Necromancer. I went in with 5/4/5/1 with 5 runes to maximize the benefits of the last two talents, and I'll probably do it again without regret. Across the Veil is just wildly powerful in the right (or, alternatively, wrong) circumstances, and Blurred Mortality and Runeskin enhance your durability so much. You even get some free spell crit for some reason. Spikes of Decrepitude is also a nice one-point-wonder most of the time, although the 2 souls sustain might not be worthwhile next time. I used it to tag things with Soul Leech so I could hit more enemies with Torture Souls, which is certainly a fun shtick but maybe not entirely effective.

Cunning/Survival -- I didn't put anything into Cunning/Survival because I'm not a fan of Track. I think it's even kind of weak as a Necromancer, but maybe I can do some shenanigans with it later. The points are definitely out there to go 1/1/1/1, and if you get Track and Adept then just get the freaking Danger Sense, it's free crit reduction.

Corruption/Curses -- I love this tree for Necromancer, it's fantastic. The Rigor Mortis Synergy, shredding 40%+ all res from anything thanks to a curse + Spell Shock, Curse of Death just doing tons of damage... The whole tree is great and well worth an unlock.

Technique/Conditioning, Cunning/Scoundrel, and Spell/Stone Alchemy -- I didn't get these trees but Escorts give notable rewards from them. Vitality, Unflinching Resolve, and Misdirection are all noteworthy pickups with Adept and your crazy spellpower plus Curse of Defenselessness means Stone Touch is going to be wildly overpowered. You can even shave off some stun resistance with a Biting Gale rune.

About Racial Trees:
As I said, I'm not actually a fan of the lich tree. Between Corruption/Curses and Spell/Master Necromancer I feel like I've got literally everything I could want from the Lich racial tree, plus I can pick up a good racial tree like Skeleton or Shalore or something and a good prodigy like Blighted Summoning or Master of Disasters. What the Lich tree *does* do is compress Corruption/Curses and Spell/Master Necromancer into one prodigy point, so if going Cornac isn't enough role compression from your category points you can go for Lich.