You have enemies? Good, that means you stood up for something.
If only you had it on the Xbox. :S
I got it the day it came out on the Xbox, oh well. The story was pretty awesome wasn't it? I'm not sure what Platinum means, since I don't have a PS3, but I'm assuming it means you got all the "trophies"/achievements, right?
If you didn't, I would recommend some side quests, there's cool post-game stories. (Some that even have cut-scenes and etc.)