Not overly-zealous Space Marines doing their thang. Solid "Humanity Fuck Yeah!" but the Grimm are without number, and just being good at slaughtering them isn't enough, and the Space Marines know it, but haven't figured out what to do about it - so although they're overpowered to their foes, it doesn't really matter.
The action is fun, but while I can imagine the Lamenters are cool enough not to purge everyone around them it's a little hard to believe that they wouldn't be trying to bring Remnant into the Imperium immediately. When there are Guard and other forces around it's really unbelievable that they'd all just fight alongside the abhumans, heretics and obvious psykers. Never mind how no-one in what government there is in Remnant side seems very concerned about talking to the high-tech aliens who just dropped in. I'd also complain that they're focused on fighting on the front-line in a million small skirmishes rather than actually aiming for a strategic objective, but GW does that all the time, so fair enough. But overall the combat scenes are well-done, with everyone's favourite chapter being awesome, so it's a fun enough read.