Outlast is easily among my favorite horror experiences of all time, letting you play your own personal found footage flick. Making the camera the main mechanic was an excellent idea, and completely culling any ability to fight back really ratcheted up the tension. Outlast remembered something that every action packed zombie game forgets: there's nothing scary about being able to obliterate the things chasing you.
Based on the recently released teaser, it looks like the religious overtones that popped up in the first game but were abandoned near the end of the story will come front and center this time around. My hope is that they keep the creepy religious themes going strong, and then at the end reveal nothing supernatural or sci-fi is going on at all in the sequel, instead letting the horror of humanity's own vile actions sink in.
Hopefully some tweaks to the formula pop up to keep things fresh and overcome the few flaws of the previous game to avoid the dreaded sophomore slump.