I have the Platinum Hits version of the game and I bought the Undead Nightmare pack separately. I just had to go to the game hub and install the Undead Nightmare pack. No issues.
Yep, it gets dirty easily. Also, mine does not play well with other electronics. Maybe it's because I use a play and charge kit, but if it's near my phone or laptop, it will often disconnect. Feels great at least.
My friends have been hyping this game up since the beta. I did the same and Redbox'd it tonight. I like it, but not enough to buy week one. It was fun playing with a friend, but I think I'm resisting starting yet another game when I'm not done with Halo/Rainbow Six yet.