Are there any single-player games that resemble Space Marine 2 in terms of their expansive environments and warfare scenarios? You even take your time walking in order to fully enjoy the immersion and sights.
The oldest Call of Duty campaigns come to mind the closest.
I got really into Warband about six months ago, playing a fantasy mod. I loved positioning a wall of crossbowmen and mages on a hill to unleash havoc on the enemy, although the sieges were quite a grind.
Are you referring to Aftermath or the first game? I have only played Aftermath, and I thought it was fantastic. The large-scale hordes were awesome, and setting up defensive positions was a lot of fun, it reminded me of Left 4 Dead in some ways.