Oh boy this is a neat class.
When it originally came out, it was pretty much the absolute strongest class. That was just the offensive side, too. However, this class has an unique defensive side.
It has your regular 3 turn stun (Though the Mage variation. No damage), but it also has Dominate. Now, Dominate is a fun one. Either the monster hits itself, or it deals increased damage on you. I think I tested t once and it's 80% shot to hit itself. Dominate, however, CAN'T BE RESISTED. It's deals the damage on itself via DoT, so if the monster has 100 resistance to it's own element, it does nothing, more than that it heals itself, less than that, 100%, or a weakness, 200%. This means you can't use it on quite everything.
Necro also has a quite handy healing skill. Not on the level of old DL and such, but still rather good.
Mystify works as a looping Blind skill IIRC. However, it has a -50 Bonus while also increasing the damage of the monsters. That... as silly as it is, might not be a bad thing.
Because this is the absolute greatest thing about Necro. Turn. Turn is a unique shielding skill, and pretty much the best in the game. It gives you 200 resistance to the element you got hit by last. Now, against a monster with multiple elements (Or multiple monsters with different elements) it's not ideal, but. At the absolute best, you can reach at least 40 All resist. This means you take 60% damage from all attacks. Now, you use Turn. Your resistance against the relevant element suddenly becomes 200 (At least) + 40 of All. You now have 240 resistance, so for the next two turns, you will HEAL a giant amount, 140% of the monster damage, more than double what the monster normally does against you.
So in end, Necromancer is actually a really good class even on todays standards. (In fact, new standards would make it worse, most likely) It has a somewhat lacking offense nowadays, but this is another great example of a class that isn't just offense. It has some rather useless skills, yes, and the offensive skills can be a gamble, but outside those it's a solid class.