To help you with some pointers, SCEA and Insomniac provided IGN with the following video on Berserks. What are Berserks, you ask? These are rewards that players gain for accomplishing their goals in competitive multiplayer matches. Initially you only have a few, but you gain multiple powers as you play more. Some of these range from being able to see heat signatures of enemies through walls to invisibility and even health regeneration for allies. If you want to excel at Resistance 2 tactics on the 60 player battlefield, you'll want to take a look here to start getting familiar with the abilities you'll be able to unleash once you join the beta.
A few new maps are shown in the video.