just finished the Alien campaign in AvP3 on nightmare difficulty. Geez...if that's the easiest of the 3 on nightmare difficulty then I don't want to know what the Marine campaign will be like
Basically each enemy is stronger, blocks your attacks much more and you can't take a lot of hits or shots before you die...but that's not all....if you die, you got to redo the entire mission again, no check points. Dang, it's like playing NES games again where you had to start all over when you died!
