Gameplay will be similar to the first with a small differences for freshness. There will be larger environments for evasion and outdoor areas will be included. AI has also been updated to be less predictable than the first.
The release date is Q3 2013, but it's been delayed from 2012 so that can always change.
I'm a massive fan of The Dark Descent. I think it's one of the best horror games I've ever played. It's terrifying. It had a free expansion, and it also has a level editor for fans to make their own custom stories (and some of the custom stories are as deep and well made as the original story). It's an outstanding game, and I'm hyped for the possibilities of a second one.