I kind of regret not reading the previous two, now that the big reveal is (massive spoilers) it's a big crossover from all their previous games and all the old characters are there, including the old protagonists (pic related). This probably would've been a crazy pop-off if I'd read the earlier games.
I guess that's what happens when you go in totally blind, sometimes you get screwed over. And if somebody actually told you 'no, you HAVE to read the previous games first', you'd probably figure out the twist pretty fast.