I find myself enjoying brief moments in the single player, and then being tired of the game for even longer moments.
Killzone: Shadowfall is gorgeous eye candy, but the single player is horrendously lack luster. I think the trophy list says it all. Half of the community has finished the first couple chapters, but it starts to drop as the chapters go on. About where the wow factor wore off for me is about the place where the chapter completion rates drop off into the teens.
I prefer my multi-player with split screen and friends in the same room, so I don't think I'll be getting too much use out of Killzone's. What I can say of the little I played is that I felt pretty darn important to the flow of battle, despite being not all that great at killing other players, all thanks to the spawning system. I could actively help my team hold a strategic position or flank an enemy's by careful placement of the spawning machine while playing support class.