So this is pretty cool as I was expecting some kind of fairly rubbish nurglified Hive population of expendable chaff. Having some IG to fight against is going to be SWEET and gives me hope for all kinds of other IG enemies maybe right up to a sentinel walker. Addin command squads, Ogryns, and chaos-psykers and we’ve got a great potential roster of enemies - especially if it’s all coupled with some true chaos forces.
HYPE
Could you explain what that enemy group is for someone who doesn’t know anything about 40K
… and crappy pathfinding, rubbish AI and janky animation… Oh, did I say it out loud?
HYPE DENIED 
This is from my non-expert experience with 40k.
One of the classical scenarios in 40k, far more so than in Fantasy (even if Chaos cults within the fold of mankind is very much present in both settings), is that Chaos does not come from outside but rather consists of former loyal soldiers and civilians who have changed side and strikes against humanity from within the human fold (there are forces of Chaos attacking from without like the Robloods in 40k as well, I should mention).
Hence relatively ordinary people who have turned to Chaos is a far more common opponent for humanity in 40k than in Fantasy.
The Imperial Guard are the “Hammer of the Emperor” and the stalwart defence against the horrors of the universe. Each world raises regiments to serve in galactic wars and the units are named for their homeworld. Cadian 492nd (from the planet Cadia), Vitrian dragoons (vitria) Tanith First (from Tanith) and so on. These are the typical men and women - mere humans - who fight to preserve the Empire. No superhuman space marines or gifted Inquisitors here just men like you and me.
as @Slayerkin described, chaos is more insidious in W40k, having cultists and corruption at planetary level. If the Planetary Defence Force, the Planetary Governor or the Imperial Guard stationed on that planet turn to chaos, they keep their equipment and fight against their former masters. This is what appears to be on the cover with an imperial guardsman, clearly corrupted with the chaos sigil on his helmet. It gives hope for lots of ranged firefights (for me at least).
Hey, even with all that it’ll probably be fun. XD I just wonder if they’re going to refine the gun mechanics to add the kind of depth that Vermintide has.