Initial impressions after playing about a half-hour:
Atmosphere is spot-on perfect. A feeling of dread permeated the entire experience.
Graphics look really great. A few jaggies though. Looking into that, as the game's options menu doesn't have many graphical features.
Controls are simple, but all work well and are smooth.
Game does include a reverse Y-axis option, which is important to me (and a few others I suspect).
The first half-hour at least is extremely linear, with lots of scripted events. I'm hoping that this will open up a bit as the game progresses. I don't expect an entirely open game of course, but even opening things up just a little bit would help immensely.

Performance:
Running the game at 2560 x 1440 on a Viewsonic VP2770-LED monitor, which only runs at 60 hz. However, even with everything maxed out, I'm still running a solid 60 fps (well, 80% of the time, I'd say), with a few dips into the 50's, so I'm pretty impressed with the optimization.

I'm all the more impressed, since I'm getting those good framerates on a 3-year-old off-the-shelf Dell StudioXPS. This machine came with Win7 64 bit, a Core i7 870 and 8 gigs ram. I upgraded the video card to a GTX 570, and the PSU to an Antec Earthwatts 750. My video drivers are very old: 311.06, but I don't update them because they've run every game I have flawlessly.

So if you've even got a halfway-decent rig, you should be able to run this game okay, I think.
I have read about a few people having trouble with 32 bit systems, but I cannot verify that, so if you have any input in that regard, I'd appreciate it.

I'm in agreement with your assessment and likely around the same point in the game as you were at the time of this posting. The bloody footprints following the player for a distance is something I find particularly impressive, along with sound when the player turns and shifts their weight. Looking down and seeing the rest of the PC is equally impressive...even though it shouldn't be. As a fan of FPS games I like the ability to see the rest of my character as if I were really there and, as immersive as games with a FPP are, there is nothing that adds to immersion quite like being able to see the rest of oneself.

With that said, there are two key criticisms that I would like to make point out that you have not and they revolve around the 'obvious not obvious' and the 'not obvious'.

Obvious Not Obvious

This is something that we've seen in video games where an obvious action cannot be taken because the game will not allow it. The examples of this are many and obvious in other games so I will not go into them. In Outlast I am led to believe that since I can jump and climb into windows and air vents that I can climb over obstacles that appear sturdy and are less arduous to navigate over. This belief is strengthened by the early demonstration of being able to squeeze through tight spaces.

Unfortunately, what seems to be obvious by similar examples is made not obvious by experience. The player cannot climb objects like stacked desks because the game will not allow it. One can make the narrative argument that these situations would make too much noise and I can accept this to a degree, however crawling in ventilation ducts that make a whole hell of a lot of noise seems to me to weaken this argument.

I do not like that I am utterly unable to close doors slowly that are already open. For some reason the player is only capable of closing them quickly, resulting in a loud noise. (If this is proven false by other players I would like to know what I am doing wrong in order to better adjust my playing and redact this portion.)

Not Obvious

Two encounters early on struck me as awkward and, for the sake of saving suspense, I will only paint them here vaguely.

In the first encounter I had to continue on even though all natural instincts told me to get the fuck out of that area and very, very quickly. I doubled back and found that the way I entered was barred from me and that the only way I could proceed was through an area I was pushed from by a fantastically scary and intelligent event. Seeing the obvious not obvious problem above, I thought I could get around it but, unfortunately, I could not. It was not obvious that I should continue in a direction of an even that pushed me back. This seems to me to be a minor narrative issue and I can only hope it doesn't continue.

In the second encounter, still early but further on, I had to hide to stay alive. Unfortunately, due to the way the cross-hair (a small dark circle or a half-again larger open circle) and text prompts work, I never knew that this was what I should do until after I died. This is compounded by the current inability to open any drawers or things that look to be containers. Finally, there is the issue of the tutorial-in-progress. When I consider that earlier prompts gave me a sort of tutorial I came to expect that in the first instance of a given thing I would be made aware to do X when I saw X in the future. Thus, there was no in-game reason for me to check a particular area -and please not that I prefer to play horror games as if I am there in the game, not playing the game in my chair- and therefore I did not. This, again, seems to me to be a minor narrative issue and I can only hope it doesn't continue.

These two criticisms aside, Outlast has a whole hell of a lot of promise and I am eager to delve into it further...I just have to wait because my girlfriend wants to watch me play it. ^.^

Talking about atmosphere... the game is brilliant. Different than first Amnesia yet with as much intensity.
One thing funny is that i refused to go on Outlast at its release because of the steam thing. But now it is on gog, i am glad to jump in. Without gog i would have just kept Outlast out of my computer.

As such, i already watched many trailers, videos and even walkthroughs of the first moments of the game.

No matter i know some parts are scripted event, no matter i saw many times this or that jumpy scary moment bound to happen here and there, no matter i am warned and aware... I still fall for the trick once playing because the game is really immersive.

Talking about atmosphere, a little joke (NSFW) about outlast that is now a running gag aroung my friends and I...
http://v.cdn.cad-comic.com/comics/cad-20130906-9d0f2.png

Question. How long is this game?.

I too found the beginning to have a really amazing atmosphere. Unfortunately later on, I completely got jarred out of it. Mainly because there are more encounters where you have to run, and if you don't take the strict single path to victory and happen to die...well let's just say after a few times dying it just becomes a tedium of finding the right path. Atmosphere gone.

Such a shame too, cause up to near the mid point, I really felt a lot of tension and fear, which was really fun. Unfortunately I can't seem to get the atmosphere back, cause now I just figure if I die, i'll restart at check point and try to find that single path to the next checkpoint...fear of dying and atmosphere now gone.