The Raptors are Raven Guard successors, and specialize in stealth and ambush just like their parent Chapter. The Raptors share the Strike from the Shadows rule, giving them Scout and Stealth on turn 1. Where the Raven Guard accentuate jump troops, the Raptors specialize in marksmanship. As Legendary Marksmen, stationary Raptor units can choose to make their bolters and bolt pistol weapons Heavy 1 and gain Rending.
As we’ve already discussed, Strike from the Shadows is an okay rule but not amazing. Rending bolters are awesome, but turning them into heavy weapons is a big price to pay. Essentially, it gives your Tactical squads much more hitting power against heavy infantry but makes them much more stationary. Fortunately, Scout works well here as it allows the squads to get into position early and make use of their Rending bolters. It will take more planning to make use of this ability, but, when used correctly, it will allow your squads to control areas of the table from early in the game.
Lias Issodon is the Chapter Master of the Raptors, but he has a slightly divergent statline. He trades a point of WS for BS and loses an attack compared to the standard Chapter Master. He also has very unusual wargear; he carries a power sword and bolt pistol and wears artificer armor, but he lacks an iron halo. More fitting the them of his Chapter, he has a locator beacon and a unique bolter, Malice. Malice can use Sternguard ammunition or can fire as a Salvo 2/4 30” range bolter, and can benefit from Legendary Marksmen. I doubt you’d ever use it as 4 shots will be better than 1 Rending shot, but it’s something to consider.
Lias Issodon also has a few special rules to aid his army. Infiltrate, Isolate, Destroy allows him to inflict D3+3 wounds with no AP to any enemy unit or D3 Haywire hits on any enemy vehicle before the game starts. The unit must be deployed on the table. This is pretty handy if you choose the right target, and can disable an important enemy vehicle or unit. Imagine hitting an Imperial Guard Command squad or Seer Council before they can cast any of their powers. Additionally, the Cunning Strategist rule allows you to re-roll any of your Reserve rolls as well as imposing a -1 modifier on your enemy Reserve rolls. Not too shabby at all. As icing on the cake, he is Shrouded and can confer this on any squad he joins. Finally, his Warlord Trait gives all Outflanking units Acute Senses, which is very nice considering that most or the army can deploy that way.
Issodon is an extremely rare example of a Space Marine HQ designed for ranged combat. He can do some damage, even before the game, provides some general buffs to the whole army, and makes the squad he joins more durable. He’s a good choice for his points cost, and supports a Raptors army well. He certainly plays differently from any other HQ option.