I only play single player and while Kill Zone has great single player campaigns, Horizon simply has a lot more content. Plus I prefer open world RPG lite over corridor shooters.
Kill Zone was very pretty though, KillZone SF did feel like a next gen game at the time.
The lighting and Madder sound processing were amazing:
I don't really have a preference, love both IPs. But I have put more hours in Horizon and Burning Shores looks incredible







