I don't believe I've actually blogged about this jolly fellow yet, so here goes.
The Wraithlord. It's big, it's burly, and it's tough. It's an Eldar heavy support choice, and instead of a graceful grav tank, it's a hefy monstrous creature.
It's also a damned spiffy sculpt. The one shown here isn't mine, but you get the idea. Without further ado...
The Wraithlord has several pros.
Toughness 8, three wounds, and a 3+ armor save. T8 means that S4 hits simply cannot wound it. Most monstrous creatures have four wounds, but they also tend to be T6. The T8 means that most S8 weapons that break the 3+ save need to see 4's to wound. Imperial plasma at S7 needs to see a 5+ to wound, and autocannons and the like need to put a decent amount of rounds to force saves on the Wraithlord.
Bottom line? T8 means the Wraithlord can absorb a good chunk of abuse.
2) Strength 10
If you end up in assault with the Wraithlord, S10 is short-hand for 'ruins your day.' If you are a vehicle and the Wraithlord hits you, then S10 + 2d6 usually sums up to 'penetrating hit.' It also tends to mean 'instant death' if you're a character. The only non-monstrous-creature that can stand up to a single smack from a Wraithlord is a Necron Lord w/ Destroyer body, just because his rules say he IS T6 with the body, as opposed to say the T4(6) that a Nurgle biker is.
3) Shooting Capability
The Wraithlord naturally mounts a pair of smaller weapons; it has two slots to fit either shuriken catapults or flamers. Translation: it mounts a pair of flamers. There's no point in ever mounting shuriken catapults. This is your Wraithlord's only built-in defense against getting bogged down by hoards of something like Termagants or Hormagaunts.
As a monstrous creature, a Wraithlord may fire two weapon systems. For those that actually consult BS to hit, the Wraithlord is BS4. Beyond the Fire Prism, it's actually the only place in the army to find BS4 heavy weapons. The most accurate weapons platform outside of the 'lord is the Wave Serpent's turret mount at twin-linked BS3 (...which actually beats BS4 with a 75% chance to hit vs. BS4's 66% chance)
The Wraithlord must take a single weapon, and may take a second heavy weapon. It can pick from any of the Eldar heavy weapons (Shuriken Cannon, Scatter Laser, Starcannon, Missile Launcher, Bright Lance) or the Wraithsword, which grants it re-rolls to hit in assault. If you really want, you can take duplicates of the ranged heavy weapon, but then that weapon is treated as a single twin-linked one. Hey, can you drop a lot for a twin-linked BS4 Bright lance! I wouldn't, though.
At the beginning of the turn, you'd better have a psyker within 6", or a Spiritseer within 12" (Spiritseers are simply Warlocks with an upgrade). Otherwise, roll 1d6, and on a 1 the Wraithlord simply stands still, does nothing, and is automatically hit in assault.
Obviously, this is a major concern. Sure, it doesn't happen often, but it DOES mean the Wraithlord might do absolutely nothing when you really want the Wraithlord to contribute to the battle.
It ALSO means that people that can crank out large blasts can potentially threaten the Wraithlord and the attendant psyker.
The Wraithlord moves 6" a turn. Sure, as a monstrous creature it gets Move Through Cover, but that only does so much. It can of course Run, but it should have heavy weapons you're interested in firing.
Bottom line? Lords aren't really that fast.
A Wraithlord is something like ~120mm tall. It is difficult to give a Wraithlord cover. A decent chunk of the ranged weapons that are worth shooting at the Wraithlord punch through the 3+ save (IE: Missiles, melta weapons, Rail Guns, Lances....).
If you want to give yourself a cover save, you're going to need a building, an Avatar, or a Grav tank to get cover. There's just a lot of Lord to cover. He's not as hard to obscure as, say, a Soul Grinder, but he's up there.
Oh, and you'll never get cover from a Vendetta. Ever. It'll smoke a Wraithlord in a turn, potentially.
4) Melee Skills
While the Wraithlord is S10 and ignores armor saves, it also has WS4, I4, and 2 base attacks. This means that the enemy can dump a large number of cheap targets into you, and promptly ignore you for the game.
It also means that a large squad with a powerfist can beat you down over a couple turns; you squish a couple of marines and then the champ punches you in the ankle, hard.
Bottom line? You have to be careful what the Wraithlord gets into assault with. Even against something like a Dreadnought, it's a dicey proposition. You have a couple chances to hit them and break them, and then they knock wounds off. S10 power weapons DO ruin your day.
The only way to augment your melee skill? Wraithsword. Get those re-rolls in assault, but you do forfeit a ranged weapon to do it. At least the sword looks snazzy.
Additionally, the big problem is that the Wraithlord is Fearless. If a Wraithlord is part of a multiple-unit combat, the enemy simply ignores the Wraithlord and beats up as many of the other units as possible. If you lose combat because of this, the Wraithlord is subject to 'No Retreat!' wounds, and the enemy inflicts free wounds on your T8 guy. Not so hot. Thus, I wouldn't necessarily always use him to bail you out.
The Wraithlord needs a psyker attendent. It is a decent gun platform, and resilient against a number of ranged weapons. It needs to be careful in assault, though, as its few attacks won't always fight off a determined enemy that brings a powerfist.
Employing the Wraithlord
Per the 'con' section, we can tell that the Wraithlord needs a psyker nearby, and melee support.
There are two ways to get this: Farseer, and Warlock.
The Farseer is a nigh-on obligatory HQ choice, and if you deploy it near the Wraithlord, it keeps the big lug honest. If you're keeping the Wraithlords near home, then something like a Farseer with Fortune in a unit of Rangers is certainly an option. Otherwise, a Farseer in a Wave Serpent (or Falcon) nearby is similarly an option.
The Warlock is your other option. Warlocks mean Guardians or Seer Councils. Well, not really Seer Councils, as those should be on jetbikes and shoved down your opponent's throat (and the Wraithlord just isn't going to pace that). The speed of the Wraithlord means it can pace Wraithguard, and the Wraithguard troop unit takes a Spiritseer. If you want to run a Guardian squad that sits on your home objective, then you can give them a Warlock with, say, Embolden and Spiritseer.
The Wraithlord does not have the speed to necessarily dictate who assaults it. You can either screen it, or if you're advancing it, you bring someone to bail it out. If you're going on foot, two options come to mind: the Avatar, and Harlequins.
Avatars are relatively cheap at 155 points, and pretty passable in melee. S6, WS10, I6, 6 attacks...yeah, he'll mess stuff up. He really benefits from Fortune with his 3+/4+ saves. He also adds another heavy target out there, which just helps Wraithlords. Good old 'rule of bringing multiple large targets.'
Harlequins are more expensive, but also more potent. They need to be taken in decent numbers (like, 7-9) and should be upgraded with Kisses and a Shadowseer. The Kisses are for lethality, and the Shadowseer is to keep them alive on foot. They'll benefit from Fortune and Doom support.
2) Wraithlord Loadout
In part, it depends on what the rest of your forces have. I always roll with two flamers; there's no point in shuriken catapults.
That aside, I've found myself favoring two combinations: EML/Scatter Laser, and EML/Bright Lance.
The EML/Scatter Laser can crank out a decent number of wounds on infantry and monstrous creatures alike. It can also hunt lighter armor. In close, it kicks out flamers into infantry.
The Bright Lance/EML is pretty dedicated to hunting armor. It throws out two S8 shots a turn, one of which is that ever-lovin' lance.
Dvering's suggested that in a 1,000pt game, a simple 2 flamer/Wraithsword lord is a solid loadout; 3 + an Avatar are about 455 (90 base + 10 for the Sword per lord, + 155 for the Avatar). I agree with him, though will point out that in 1,000, you don't necessarily have enough points for a balanced army. It's a LOT of T8 wounds to deal with, though, and unless they did something like bring Sternguard and their 'wound on 2+ ammo'...they're screwed unless they can outrun you. Still, I think once you get to a more reasonable size like 1,500, the Sword-Lord loses some of his draw.
3) Army Composition: Integrating the Wraithlord
Wraithlords are by nature slow. You can commit to something like Elfzilla, save that it's slow. Any way you look at it, to properly support a Wraithlord you are giving up speed. By its very nature, you can't just toss a Wraithlord into your build willy-nilly; the speed and the Wraithsight see to that.
If you're going to go pure foot, I'd go ahead and commit to triple Wraithlords and an Avatar and Farseer; this means soemthing like 700 points or so, and takes your heavy support and HQ slots up rather neatly. I won't conjecture that it's a good build or not, but you might be in for an uphill battle. A heap of T3 fellows isn't exactly durable, even with cover.
If you're going to partially mechanized, you still need to find a way in your list to leave psykers behind to 'tend' to them. Elfzilla/Wraithzilla neatly covers this with the Spiritseer in the Wraithguard. Other partial-mech builds are likely going to stick either a Farseer/Ranger in the back with them, or Guardian Defenders with a Spiritseer.
Wraithlords in Summary
Wraithlords are hefty gun platforms that, like most monstrous creatures, are more durable than they are killy. They are capable of ripping vehicles apart in assault, though can get bogged down by numerous troops and killed by some assault specialists anyways.
They are capable of putting out respectable ranged firepower at range, and dealing devastating damage with flamers up close.
However, they have special support requirements beyond the simple melee needs, and getting psykers near them is important.
Overall, they have some special needs in terms of build that make them more difficult to use than tanks, and they commit you to a slower, more durable detachment if not army as a whole.