Same story. Just received the game from Amazon a few days ago and after playing the single player for awhile I wanted to give Multiplayer a go. Before my first match I downloaded the compatibility DLC, one that gives me access to the Hoboken Rooftops, and I believe the other free one was called "Gorilla Warfare". I noticed immediately I was just a floating gun but I figured there was some sort of compatibility issue with an update I didn't get or less likely this was the way it was supposed to be so I'd have a better field of view. It wasn't until I noticed I was doing way too well for a newbie and then another player complaining that he couldn't see me that I realized it was a bug giving me an unfair advantage.
I dropped out immediately because I didn't want to play that way either and because I was a little worried I'd be reported and penalized for exploiting. I'm relieved to find out that it's a "known bug" and that I won't find myself in trouble over this. I figured I'd post the details of what took place step-by-step in-case the right people read this and in the event it's helpful in resolving the issue.
I should also point out that I noticed that none of the character models were showing up when I was trying to view the Avatar options(Locked or Unlocked) before my first match. I saw the background but nothing else for the male or female versions. I opted to play as a male soldier with the first available avatar option. My first match started me in at the last few minutes of a Team Deathmatch round on the Branco Offices Map. The second match was the Hoboken Rooftops Team Deathmatch map.