So ,looking at tech demo and overture videos I can say that game need:
1.NPC's .like old mineworker trapped who need rescue etc ......
We should have a little town also
  Have little bunnies for sale also^_^  You can do little quests such as find a missing ring and other stuff also
Serious now; What happens when you find the miner?  Does he prance away never heard from again? Does he go out to get help?  Does he follow you around?  Once you found him you know others might be there and the game woudnt' be so scary and alone.
2.Better animations and better weapons .That pickaxe in video was done very bad .I wish to attack with mouse moving ,not by clicking a button and starting an annimation(something simillar was done in Trespasser) .
I'm not a programmer or anything, but as far as I know it's hard to create animations that look real.  The official game, Penumbra Overture will have something like that, ask dark reaver on it though;  the people who make the game talk to him.
Too much weapons will kill atmosphere ,but if I have a flashlight, keys, and some things around me (chairs ,bootless...) why I can't use it ??? I tried (in tech demo) throw something at the bats and nothing ...only dynamite and that puzzle killing(good idea with it ,but it shouldnt be used with every monster).
This is a tech demo, not a full game.  I'm sure it's hard to impliment a fighting  system that's fun, balenced, and difficult at the same time(You don't want a easy fighting system in horror games aimed for a older audiance I believe)
3.The game is too empty ,just add more objects.
This is a tech demo.  I believe they were in highschool or something.  This is a 4 man team also.  The game has insane compooper requirements, more objects would take more cpu power. Â
4.Maybe if game is realistic(I think it is and should be) you might add legs. but that is optional becouse if you add legs you also gonna add hands so..its too much work and almost impossible to add hand that perfectly fits grabbing each object.
Maybe if game is realistic       This is one of (Or most) realistic games I have ever played.  I'm sure it's very very challening and difficult to program realistic phisics in a computer game.  You just don't talk to the computer "Alright, I want real physics.  Do it"  You need to add code and such.  You don't really need to add feet.  When your walking, do you really notice your feet?  It would also look kinda stupid to see your feet, this isn't a 3rd person game and unless the charecter leans backward when he walks, he isn't going to see his feet.
The don't want your hands to be swining all around.  You see the hands when you hold something(The new videos on the official game show breif moments of the hands, they look 100x better than the demo it seems)
5.More commercials - 90% of gamers don't known that it exist !
Wow.. 10% of gamers know about thisO_o  And only 2 commerials and such.  I think that's really good.  Low budget advertising has really worked wonders.  I was told this, you don't want to over-hype a game.  It also costs money to advertise(That's where websites get most of their money, companys pay them to show stuff)
6.Think of good story that anserws what monsters are. Please only not and UFO like it was in call of cthulhu dark corners of the earth.
The story is this;  Someone was picking their nose and something really nasty came out.  The scientist who picked it put it in dirreaha and blended it together;  thus creating the monsters in this game.  That's a joke, but the people are trying to make this game realistic.  They arn't (Hopefully x.x) going to have over-used ideas.=/
Sorry for my bad mood, not really in a good mood right now because I think my depression is coming back-.-Â Â
Sorry for any spelling mistakes also..
edited part: And your putting the topic title as if it's a FACT. I understand people's opinions are different than others, but your like OMG IT HAS TO BE THIS WAY BECAUSE I SAY SO AND IF IT ISN'T ITS GOING TO SUCK SO U BETTER LISTEN TO ME. Kinda annoying(I bet this post will get me banned here>.>)
Sometimes, if you look carefully at a wall for a few minutes, you'll realize you wasted some time.  It's true.