Just spent 1 hour 40+ mins to complete the tribute map with 4 people on xbox360 and all I can say is wow well done gearbox.
There are 30 waves to complete and the size of the tribute map is about 4 to 5 times the size of the level no hope in Hadley's.
Everything is there from the north lock to the south lock with medical and operations it felt like the whole colony from the film.
The xeno AI is quite good and the later level's the xeno's get really hard as they attack very quick and take a lot of ammo to take down they are like purple soldier xeno's with a different head style from MP.
Wow that map sounds huge!!