if you're not into the action of a game and only the story than perhaps you should read a book or watch a movie or TV show instead. if you want the interactive portion than companies could consider an interactive comic type of alternative. like what was done with the original Mass Effect. the reason why they made that was so that people could have a personalized gameplay file going into ME2 without having to spend the massive amount of time playing through the actual game for 100% of it's content.
for the regular bersekers, use the flamethrowers that spawn for you. while a couple of people on your team flame it, the others shoot the crap out of it. for the lambent zerker i think you do the same thing but can also shoot the glowy spot on it's front.
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