The Necromancer is Underpowered Reason 2: Everyone else that uses magic damage is better at it

The necromancer, like the other classes, has three skill trees. Later, I'll elaborate more on curses, which aren't really viable as anything more than utility, and summoning, which has its own problems. The poison and bone tree is the one that gives the necromancer offensive spells. Bone spells do seem to have certain advantages over poison. Firstly, there are more synergies here, which means investing heavily in bone spells improves their damage incredibly. Secondly, they offer better defensive capabilities. Poison can, well, poison monsters and nothing else. The bone skills offer a shielding spell, walls, and the ability to strike from a greater distance. And finally, they do magic damage. Poison immunity is very common in Hell. Magic immunity is the rarest immunity for monsters to have, meaning that a character that relies primarily on magic damage can run around in Hell and generally ignore those "immune to..." labels on everything.

Synergies are the key to using the "bone" portion of the poison and bone skill tree. The increase in damage output from synergies is massive. But compare it to other classes. Most of the other characters don't have any source of magic damage. The amazon has Magic Arrow, but the magic damage there is an afterthought, not a primary killing method. The assassin is in a similar position with Psychic Hammer. Two other characters have access to a single magic damage skill that really is all about magic damage: the barbarian with Berserk and the paladin with Blessed Hammer. They both completely outclass the necromancer. While the poison necromancer gets more poison skills than other classes and can get more raw damage, but loses out on versatility, the bone necromancer, with far more investment into his magic damage skills, actually gets less damage than other magic specialists. And yes, he's still less versatile.

Using Berserk, a barbarian's weapon damage is factored into the skill damage. Berserk has two synergies that improve the damage, but most berserkers only max one of them anyway. The rest of the skill points can go into typical barbarian skills, so that you can dominate everything in your path. When a berserker runs into magic immune monsters, he can easily demolish them with physical damage from Concentrate, Frenzy, Leap Attack, Double Swing, or whatever. Probably Concentrate, though. So yeah, more magic damage than bone skills, and easy access to skills that can absolutely wreck magic immune monsters.

Blessed Hammer has two synergies, like Berserk. When I made a hammerdin, I maxed both of them, so that's more investment than a berserker would need, but still a lot less than a bone necromancer would require. The main advantage to Blessed Hammer is that paladins get the Concentration aura. With Concentration maxed, Blessed Hammer does far more damage than bone spells, and flies all over the place, killing everything on the screen. Blessed Hammer no longer ignores the magic resistances of anything (before the latest patch, it ignored the resistances of undead and demons). But almost everything that is immune to magic is undead anyway, and the paladin's Holy Bolt, which is enhanced by points put into Blessed Hammer, does affect undead that are immune to magic. But a hammerdin can easily mitigate the immunity problem with Smite, Charge, or Zeal. Smite really only requires a single point and is improved by Holy Shield, which a hammerdin should be maxing anyway. And that Concentration aura will still work wonders with whatever combat skill one chooses to deal with magic immunity, improving the damage of those skills by even more than it improves the damage of Blessed Hammer.

It's true that this issue only applies to bone necromancers, but dammit, these skills take up most of a skill tree. They should work. Barbarians and paladins, on top of having far more options to increase survivability and to deal with magic immunity, also get far more magic damage for a smaller investment in skill points. That's just wrong. Oh, and did I mention that these are some of the coolest looking skills in the game. Bone Spear and Bone Spirit look awesome and are a big part of the appeal of the necromancer.

Blizzard should just fix this one. At the very least, the bone skills should get massive damage upgrades. Better yet, there could be a curse that actually works with them, because that's the real problem here. The barbarian uses masteries and such to improve damage from his skills, including Berserk. The paladin uses auras to improve damage from his skills (specifically the Concentration aura in this case, although Fanaticism and Conviction are the more prevalent ones for paladins that are not hammerdins). The necromancer's analog to those enhancements is curses. He has a whole skill tree devoted to curses. He has Lower Resist for elemental and poison damage. He has Amplify Damage (or Decrepify) for physical damage. There is no curse that helps the bone skills. And there is no reason not to have one. My preference would be Decrepify. For some reason, that one makes the most sense to me. But there should be some curse, any curse, that lowers magic resistance. Since there isn't, the bone necromancer is completely outclassed.