It does this inexplicably. I've had the game start off NAT: Open and then after some games get back to the lobby it says NAT: Moderate. Yeah, cool, so my NAT just changed mid game did it.
So just to prove my NAT is open I'll back out of the game, do the XBL connection test, and low and behold, it's Open. I can do the connection test before even starting playing the game and my NAT will be fully Open but when the game loads the game says Moderate.
It's like they learnt nothing from the last game and the beta's.
As for my connection, don't bother. It isn't my connection. I'm on a 60mb fibre optic connection with a 6mb upload. My ping is usually about 12ms with about 2 to 5ms jitter and always zero packet loss. Are my ports forwarded? Yes, but that's not even relevant anyway because my 360 has a static IP and is in a DMZ.
Sort this trash out please.