They serve as a nexus between the two videogames, or sort of, because the truth is that they don't add too much.
We're given small hints of the four characters, both of their motivations and their past, but nothing ‘revealing', just small details.
The scenarios are mostly new, but as in the game, with a similar theme and the same post-apocalyptic aura.
There are no new enemies, but almost all from the videogames appear. My disagree with this is that some of them are too forced inside the comic, just appear for a few pages and do almost nothing apart from "hey, I'm another foe from the videogame, just in case you forgot this is GoW!".
That said, the comic is not bad. It has fantastic drawings, the locust are frightening and Marcus looks even more badass than in the game.
It's just the feeling of "really I'm not being told anything, I'l just watching a collection of references to a game with pretty drawings"... But maybe it's only my perception.