I just finished playing the demo. I played it 4 times at TGS, but couldn't beat the dog, this time I could do it. I finally got how the parry system works, and I gotta say it's really good, really rewarding when you get the right timing and counter the enemy attacks. Basically, whenever an enemy is about to attack you, a red laser will come out of his eye, that's your hint. But if you react too quickly, Raiden will just go into gard mode and parry the attack. If you time it properly, he will parry then counter attack. Now, when you're fighting a group of enemies, some of them are outside of your screen, but you can still see the red laser flashing, indicating in which direction you need to parry. Works really well when you get used to it. If you can manage to get behind (or on top) of enemies without being seen, you can stealth kill them with circle.
You get ranked at the end of every small battle. You can collect the enemies's left hands and give them to the old man Doktor (in game currency maybe?). He collects them because of the chips inside or something like that. You also have to collect the fuel that runs the cyborgs, didn't really get why though.
Graphics aren't bad at all, especially since you can cut almost everything in the background (and use the pieces to climb somewhere higher for instance). It's silky smooth at 60fps, so there's that. Lots of crates, you can find health items in them. One thing that sucks though is the black screen (loading) between cutscenes and gameplay (MGS4 did it better).
There is a lot of information in the codec calls, surprising for a demo. Lots of references to MGS2 and 4 obviously, and even a few inside jokes here and there. And there's a hidden item in the tutorial that's kinda hard to get it's a cardboard-box