Well, I went ahead and got Xul, the newest Heroes of the Storm character. I guess you can't keep me away from a cool necromancer character.
Xul is a melee specialist who is a whole lot of fun (and depending on how things turn out, might be due for some nerfs.) He has good control, a nice baseline survival ability, and a trait that makes him great at solo-pushing lanes (it's a weird kind of mirror of Sylvanas.)
So let's get to his abilities!
Trait: Raise Skeleton
When an enemy minion dies near you, it will rise up as a skeleton to fight for you. You can have four skeletons at a time. These guys are pretty weak, but they'll help you overtake the enemy's minions pretty quickly and are great cannon fodder.
Q: Spectral Scythe
This is a funky kind of reverse skill-shot. You click a targeted location in range and after a second your scythe appears there. It then travels back to you, damaging (for a pretty solid amount) anything between you and its starting location. You can move after placing this to effectively give it a longer range, and it cuts a decently wide stripe, making it great for damaging a whole pack of minions.
W: Cursed Strikes
This empowers your scythe to deal more powerful, wide-ranged area attacks which also slow the target's attack speed by 50% for two seconds. The buff lasts four seconds, which seems to give you 5 swings. This hits pretty hard and has a large range.
E: Bone Prison
Target an enemy and, after a couple seconds, a bone prison will appear to lock them down. Given the delay, you'll want to hit them with this pretty early in a fight to prevent them from escaping (or allowing you to.)
1: Bone Armor
Baseline you get this additional ability, which gives you an absorption shield. Your first talent selection will allow you to modify this to either be more powerful and on a longer cooldown, slow nearby enemies, or explode for hefty damage when it expires.
After a short wind-up, you'll radiate poison missiles to enemies around you, poisoning them for a pretty big chunk of damage over time (a great team-killer.)
Summon four skeletal mages in a line who will attack and slow enemy heroes who try to pass by them, lasting a hefty 15 seconds.
I've only been able to play two games as Xul so far (long queue time probably due to him being the newest character,) but I've found that he's very good at soloing lanes, and he puts out enough damage to duel with opponents. Using Bone Armor at the right moment is an important survival skill. There are a lot of talents for Raise Skeleton that can make you pretty self-sufficient, giving mana and health back when you raise them.
Don't overextend on Xul - you won't really need to, though, as Spectral Scythe will give you a decent ranged attack and Cursed Strikes will allow you to hit enemies relatively far away. You might be a bit less useful in objective fights - mercenaries and map-specific enemies won't get raised by your trait - but Bone Prison is a fantastic control spell and Cursed Strikes can really harm auto-attack heroes like Raynor or Sgt. Hammer.
Anyway, if you felt that Nazeebo, Arthas, and Leoric hadn't quite satisfied your "leading an army of the dead" fantasy, Xul absolutely scratches that itch.
After playing a bit more with him, it's clear that this guy has a lot of control options. While the poison damage on Poison Nova is fantastic, the control offered by Skeletal Mages is also a wonderful complement to Bone Prison. Pairing Xul with a bursty assassin like Greymane will make you horrifying to your enemy heroes. While Xul can totally push a lane on his own and go head-to-head with bursty glass cannon-types (between Bone Armor for defense and Bone Prison fro control, burst-assassins like Li Ming should be very wary of Xul) he's also a great help to group fights. Obviously, his control abilities (including Cursed Strikes) help out a lot, but also if you get some enemy minions into the mix there (like if they're trying to push on your forts) he can very quickly turn the tables and make enemy heroes regret bringing their minions along.
I tend to take all the raise skeleton talents (I'll have to experiment with other talents to make an optimal build, though honestly, pouring everything into the skeletons seems to be working ok for me.)
Also, as a caveat, I'm a PVE'er in Heroes, so some of his tricks might not work so well against other players. Still, nothing's on a horrifically long cooldown, and he hits hard enough that players are going to have to be clever not to get ensnared by him and chewed up by skeletons.