I didn't like the story, not cause it's in America. I'm Cuban. Just didn't make much sense to me. Also the ending broke the game for me. What made me love the game none the less was the coop. Playing it with my wife or daughter made it so much fun I never thought once about the story to be honest. But, when I went to the multiplayer I loved it. Reminds me of far cry 1 team deathmatch or far cry 2. Clean, simple, oldschool. No perks, no bs like they tried doing with far cry 3 which made it look like CoDMW3. I hope people continue playing the multiplayer for a long time. Cause I know I am.
Actually if you read the perk skills, some/many carry over to MP play. They may not be obvious but you use the same character in MP that you have in your SP game. So things like faster gun swaps, and I think more ammo all carry over to MP. Now you don't have to choose them as they are from your SP, but they do include perks in MP.
Glad you like the MP....personally I like the coop romp, but found most MP boring after a day or two...