Adding Western characters is to add to the feelings of isolation and terror -- when a Japanese and Westerner get stuck together, communication trouble is inevitable and only adds to your situational frustrations. The release structure as episodes is to give players the feeling of participating in an event; a TV drama they play.
As for gameplay, sight-jacking is a split-screen affair now. You can move your character while checking out the enemy positions at the same time. Unlike other survival horror games, Siren is keeping itself away from "action" and more towards "survival" -- that is, scares and story. The difficulty has been toned down, since the first was infuriatingly difficult. There's a ton of more information to read up on if you're interested as well as some of Toyama's personal opinions on the horror genre, influences, and what scares him the most.
