Just played offline this morning...and I think I am addicted. Probably the best thing about the game so far.
What I liked.
-First level I chose was Tribute, awesome, straight outta the scene where the marines enter LV-426's colony
-You have to kill aliens to acquire cash, which allows you to go to ammo drops, health stashes, sentry turrets, door bypasses, etc
-How f**king hard it was. I made it to wave 4 before getting my ass kicked...ON SOLIDER MODE. This is definitely something to play with at least 3 people. The aliens were VERY hard to take down by wave 3-4. I was shooting grenades and they would go down and rise back up. It was wild and challenging.
If I did not have to be studying for exams I would have played all morning. I can't wait to boot it up with some friends. I know people are pissed at ACM and what not, but this DLC add-on is pretty good. At least consider getting this and not the season pass.
Hope to play with you guys eventually.