Background.
"Samus. That's the only name you'll hear. Samus. It means the end and the death. Samus. I am Samus. Samus is all around you. Samus is the man beside you. Samus will gnaw on your bones. Look out! Samus is here." [Horus Rising, Dan Abnett].
When Samus was introduced in the first book of the Horus Heresy, I thought the daemon came across as independent: a terror orientated one rather than simply a murderer. This explains why he slots in to the
resplendent terror dominion in the game. Samus operates by possessing people and then turning on their allies. Simple, but effective. His fuller history -- to extensive to write about here -- is found in the Horus Heresy novels and is not limited to simply the action described in the first book of the series by Dan Abnett.
Strengths.
I really like the Born of Murder special rule that Samus has. It is highly characterful for this miniature and the background. In essence, if a character model is killed, Samus can use it as a nearby warp rift on the subsequent turn.
The whispers of madness rule is what sets Samus apart though. He directly inhibits the reserves of the enemy, makes blessings harder to cast and causes enhanced fear as anything without stubborn or fearless halves their leadership score to charge Samus, or whilst in combat with him. This is crazy powerful.
In addition to this, he has a very strong (Primarch like) stat line, combined with eternal warrior and a suite of emanations of horror to help in close combat.
Weaknesses.
As may be expected, he can only be used in the resplendent terror dominion, and must be the warlord. His warlord trait is curiously Khornate: the path of blood which means he will almost always make his charge thanks to the mechanics. Although not strictly a weakness, it does mean playing Samus in a certain manner, and hence is restrictive, rather than weak.
Other than that, Samus costs like a Primarch. This is no surprise, but worth noting.
Overall.
Samus is a very powerful miniature to play on the battlefield, with or without the born of murder rule. It can really mess up enemy armies that are reliant on deep strike (descent of angels, or terminators) and is very strong in close combat. Aiding this is the speed of movement and charge distance modifier thanks to the warlord trait which will usually be something like 11 inches according to my calculations. A very worthwhile choice for anyone wanting to play independent daemons really.