One of the best things about the 5e codices (codexes?) is that the GW writers seem to finally understand what players want. I think what most players want is to field an army that is fun, competitive but also feels unique. One of the best ways GW has managed to do this is with the FOC switch characters. The Dark Eldar start with two cool, but rather straightforward troop options. However, with a little investment, you really have 4 options. This post will examine the two alternate troops and their unlock characters. Let's start with Haemonculus/Wracks
Haemonculus
The Dark Eldar have one of the better killy HQ options in the Archon, but in 5e, HQ is all about utility and the Haemonculus is the utility HQ. First, he unlocks Wracks as Troops which we'll examine in a second, but here's a spoiler, it's good. Second, he brings a "free" pain token to a unit of your choice (remember, IC can take and leave pain tokens as they join and leave units most of the time). Finally, he has access to some exotic wargear you can't get anywhere else. Oh, as a bonus, you can have 3 in one slot. I think you'll see at least one Haemonculus in any non Alpha Strike or Bust (Vect plus the Baron) list.
Let's take a closer look at what you really get. Statline is trash. He's basically a 2W IC Space Marine Sgt. Ld 9 would have been nice. The free pain token is money in the bank. I think the best use is to have him start with a CC unit like Incubi or Wyches to toughen them up a bit. 3+/FNP and 4++/FNP are both very nice. Both units also benefit greatly from the FC on the 2nd token. Let's talk upgrades. 2A, WS4 and full price CC upgrades make GW sad. Personally, I'm inclined to go Venom Blade and call it a day. Now, what about arcane wargear (how Fantasy of you, Haemonculus). Liquifier Gun (an APd6 flamer) and keep both my CCW? Sign me up. Shattershard (template, remove without any saves unless you pass a Wounds! test, one shot) is money also. Webway Portal won't be in every build, but the Haemy is a great carrier in portal lists. Finally, the Crucible of Malediction (psykers in 3d6 take Ld or are removed, no saves). In an army without any other psychic defense, I think it's worth the points.
What's missing? First, grenades. This will become an issue when we get to the Incubi, but needless to say, this guy would be amazing with some grenades. Also, transport options. I imagine they wanted to avoid jetbike/WWP shenanigans, but the the Jetbike Haemonculus was a cool option in the old codex. Hate to see it go.
How would I run him? I think my go-to loadout would be Venom Blade, Shattershard, Crucible for a cool 90. Possibly run 2, one with the Crucible and Liquifier, one with the Shard. The bare bones Venom Blade for 55 is viable too.
What about the Ancient? I don't think the upgrade is worth the points. If you want a CC character, spend 30 more and bring an Archon and a regular Haemonculus. If you want to bring him, the Flesh Gauntlet is interesting. If an Archon could take it (and get it to 2+ poison) I think it's a viable option, but I think 4+/PW(agonizer) >> 4+/ID (FG)
Wracks
Everyone is very excited about Wracks, but I think we need to temper our enthusiasm just a tad (and let's not freak out and moan that GWvsJohn thinks Wracks suck). They're 10 points and bring a marine statline, 6+ armor, double poisoned weapons, no shooting and a pain token. 6+/FNP is pretty close to a 3+, so, in my mind, they're poison Assault Marines who score. At 10 points that's good, but not "OMG must include" good. They can also bring 1 Liquifier/5 guys, which I also approve of and standard Champ/upgrade options, which are probably best left at home (again, bringing him for the Ld might be worth it). They don't come with grenades and they can't get them easily, so that's a legit complaint against them.
So, final verdict, take them or leave them? As Elites, leave them. As Troops, take them. They fill a 3rd role as Troops (warriors=shooty/backline, wyches=CC/frontline) being more survivable than Warriors and Wyches. They're the tough, take objectives Troops option. They can also take down MC with their poison and tie up non-PW units. As an aside, I like that Dark Eldar have two comparable Troops squads in Wyches and Wracks that can do a lot of the same things (non PW assault units), but also some different things (Wyches seek out PW units to lock down with 4++ while Wracks can tie down non-PW units).
So how to run them? First, take as many Liquifier guns as possible. Second, leave the Acothyst as home. I see 2 options (neither of which are particularly difficult to figure out). First is 5 Wracks, Liquifier, Venom, extra Cannon. A neat 125, very strong anti-infantry and scores. Second is 10 Wracks, 2x Liquifier, Raider, Flicker. 190 for a somewhat tough scoring unit with legit duality. Either squad can drop a man (and a Liquifier) and act as a bodyguard/free pain token for your Archon (should you bring one). I think the larger squad makes more sense in this regard as you don't want to lose all your Liquifiers. One last option, which I think might have potential, is to bring a min squad (3 Wracks) for each IC you bring (especially non-Haemonculus IC). The IC can "steal" the Wracks pain token and leave the squad turn 1 to join their real squad (Haemonculus would start with a squad, leave it and his pain token turn 1 to join the Wracks, then steal theirs turn 2) . The Wracks then run to the nearest objective and go to ground. This can hurt you in Kill Points and leaves your Archon (or other IC) possibly exposed turn 1, but only costs 30 points.
Now it's time to go Back to the Future (2)!
Baron Sathonyx
Another utility character? Amazing! He unlocks Hellions as Troops and adds +1 to the first turn roll. Pretty good and can synergize with Vect (4+ seize) for a very high first turn probability. Is it worth over 100 points? Not really, so what else does he bring? Archon stats -1 (weird how DE have 2 "hero" level SC, but can't bring a normal Dracon anymore), shadowfield (nice), grenades (a rather pricey upgrade for units), s6 on the charge (but no PW), reliable hit & run and stealth for his unit (which doesn't totally synergize with Jump Infantry's hatred of DT). Is he worth it? I'm tempted to say no at this point. If you really want Hellions as Troops, then obviously he's coming. I haven't written out any pure Alpha Strike lists, but clearly there's some potential there. Really, his value comes down to how good Hellions are as Troops. So let's look at them.
Hellions
I've seen a lot of people get very excited over Hellions as Troops, but frankly, I don't get it. When did T3, 5+, on foot become something we want? IG bubles are an exception due to Stubborn/PW spam and heavy weapons. Hellions bring, um, Hit & Run and combat drugs? H&R and I6 is good, don't get me wrong, but even charging all the time, you still hit as hard as vanilla Assault Marines (plus the assault 2 poison soften up volley). Combat Drugs have potential, but if you're running a drug heavy army, you need the Duke also and that means no Haemonculus. The Helliarch is mandatory as you NEED grenades. The Stunclaw is cute, but I think the Agonizer is a better option. I have a feeling this might be a unit I'm missing the boat on, but I'd say leave them (and thus the Baron) on the shelf. If you insist on running them, I'd bring fewer, bigger squads to spread out the Phantasm Grenade Launcher cost and better protect the Helliarch, since he has all the grenades.
To sum up, I think the Haemonculus/Wrack combo has a place in most DE lists while the Baron/Hellions is more for theme lists or "gimmick" lists (ie pure alpha strike)