I'd still compare them. Penumbra has better puzzles and I find the atmosphere in the game better cause, in Overture, there is no escape, just trapped in a mine with no known escape. Amnesia's puzzles aren't as good, but the effects and sounds are amazing, but with all the windows, you kinda have that sense of freedom of the outside world (I'll stop going on now
). Look at some of the other forums for some ideas and just list about 3 or 4 different points for each.
With future plans, nothing yet. Got some screenshots/video of a terrain generator for the new engine, so I'm expecting it to be a bit more free roam with larger places to explore. Nothing on creatures or settings or a name, but they have said that it's not going to be as "horror based"