I just played what I think is the whole demo; it doesn't actually END...you just sort of keep running from portal to portal and after much exploring and button clicking to make sure you haven't missed some hidden quest you say "Well...I guess that's it."
The whole demo took me about 90 minutes to play and I explored everything after I killed the monsters.
I hate to echo others b/c it makes it look like I don't have my own opinion.
I do have my own opinion...and the game is "Meh."
I'm really disappointed!!!! Seriously. I have been looking forward to this game for a long time. If you watch the trailers you get psyched. Then you play this SP demo and there is no "DRAMA." You don't feel like "Ooooooh! I'm gonna fight the devil hordes and save the world! What a cool cutscene! Sign me up!' Etc, etc, etc.
It didn't crash on my system. Levels loaded quickly. "Background-task-wise" it ran w/o a hitch, and that's good.
The menu system/button system (i.e. move this thing to this slot and do something/click this to use this) is totally messed up. Almost every single shooter that has a ranged weapon/weapon w/a scope uses right-click to zoom. In this game it's "2." As in the number 2.

WTF?
I played with the graphics maxxed, just to see how it looked (as opposed to wanting smooth visuals) and the environment is nice. Smoke, in particular looks real. If you move to the other side of a barrel w/a fire inside it, the objects on the other side look blurry. Very realistic. Weapons effects suck. This gun shoots a small fireball with no splash damage. This other gun here shoots a big fireball with big splash damage. How original. I'd prefer basic 9mm/M16/Grenade launch/Rocket launcher/Redeemer weapon scaling to this crap.
But the guns, zombies, crates, walls, buildings...they look cheap. Enemy AI is non existent.
As long as you stay outside the predetermined, invisible circle of "OH, I see you!" they don't even know you're there.
The game has lots of cool ideas though. Upgradeable weapons and armor, relocator device, upgrade point system and 100 places/skills to put said points, lots of special "one off" weapons. But it just doesn't grab you.
The weapons in the demo suck. The enemy actions are so obviously "programmed" for lack of a better term.
You can count on the same type of enemy behaving exactly the same, running the same zig-zag pattern towards you, taking the same number of shots before collapsing and making the exact same sound when dying AND falling into the exact same position. No ragdoll effects here.
I won't be spending $50 on this. When it's $20, I'll buy it for sure but other than that, no.
My two cents.