I fully understand where you are coming from with the multiplayer comment, and to be hones I feel the same way sometimes, but still MP is a lot more fun then SP for me because of it's dynamic nature. You never know what you get into. I know the slaughter is not fun when you get no chance to shoot anyone in a MP game or whatever but that is not always the case, especially not with less popular games. The coop MP is another awesome MP mode that you can enjoy without worrying about your "skills" in MP. That is where the "horde mode" shines in games like Mass Effect or the new addition to Team Fortress.
With that said some days I rather just play some SP instead of getting schooled by some 12 years old that sits home all day plays CoD.
Just don't take it too serious, sit back and enjoy it and if you don't just quit and find another server. Hope to hook up with you for some coop sometime.