Honour with honest toil, Master forge-men, and duty. The Salamanders are almost the polar opposite to the likes of the Night Lords in many respects. And added to this is their terrifying visage. In the older literature, the Salamanders are pictured as largely African descent marines, but in more recent times (forgive me: I'm a very old timer!), this has had a bit of a retcon to say that their skins are simply jet black due to upbringing on Nocturne coupled with the Primarch's genes. Like many of the loyalist legions, they look a bit horrific, in this case due to the red eyes. If the space wolves are the good guy werewolves, the Blood Angels the good guy vampires, then this makes the Salamanders the good guy devils with their eyes. I kind of like this: the good guys having some draw-back or obvious physical negative about them that makes them initially look like bad guys to the people they're supposed to protect.
But I digress. How do the rules in Massacre shape up to this background for the Salamanders Legion?
Firstly, and very uniquely, the Salamanders have a Strength of Will that renders them immune to fear. They also gain a bonus to pinning and other morale checks. But I want to return to the original point: immune to fear. I cannot underscore enough how brilliant this is in a 30k environment. Recall that no space marine has And They Shall Know No Fear in 30k. The effects of fear are therefore huge. Particularly if playing against the likes of the Night Lords - thats a legion that can rout an opponent off the table in the middle turns if played right. But not the Salamanders. They will stand firm, because that is what is demanded of them. (Heck, it should be demanded of every space marine, but let's not be too pedantic). Summary: awesome rule!
They also have the Promethean Gift. This gives another amazing boon army wide: +1 S to all flamers of every type (including vehicles) and -1 S to flamers used against them (again of every type). This really begs that the Salamanders select and use flamers wherever possible and will make them terrific are getting enemy units out of fortifications and tackling them head on at close range. Coupled with the above rule, it also means that smaller sized units can and should be thought about (since they're not going to be fleeing anytime soon due to fear).
Being Nocturne Born, the Salamanders are at a severe penalty to sweeping advance rolls, and a minor penalty to run and charging distances. I don't think either of these is merited by the background material personally. But there has to be a negative to balance the superb advantages that the above rules provide. I regret to say that this is a HUGE negative as well. They're not going to sweep opponents regularly (particularly other marines), and they're just plain slow against others like the Emperor's Children. So beware how you play them.
Taken together, I think I would be playing the Salamanders are multiple small units (unlike most other legions), with a mixture of close combat and ranged weapons, and a focus on flamers where appropriate (and without going too overboard due to the negatives of being Nocturne Born.
In addition, they also have some nice war gear that they have access to. This includes artificer weapons for any character at a small cost, dragon scale storm shields for any terminator or any independent character - making them able to be storm shield / thunder hammer combination terminators (unlike regular legion terminator squads), they can buy eternal warrior for any praetor and they always have the option of switching out heavy bolters and twin linked bolters for heavy flamers and twin linked flamers. Or perhaps you prefer an inferno pistol to a plasma pistol - done and done for the Salamanders.