I have the platinum, it was a huge chore. The game isnt hard, even on the hardest difficulty, but there is a painfully huge amount of things to collect, some of which you only get one try to get. Once you finish the level, there is no going back so you have to start the entire game over. Not all of the game is open world. There are some (for lack of a better term) rooms for mini-quests, that, once completed, lock you out completely.
When I played (probably a year ago) getting in a full room was impossible. I cant imagine many, if any, people are still on. So if you're thinking of getting this, I'd say you have little to no shot of getting any online action.
If you're just going to play through the story, shoot some Nazis, earn a quick batch of trophies/achievements, and shelf it, it is probably worth the $10 or $12 you can find it for. Just don't expect a masterpiece, or any online activity.