This aspect of it really intrigues me...it just sounds fun as hell to leave good stuff and misleading notes behind for other players.
It really is quite interesting how this works.
Obviously I'd prefer a system where I can team up with my friends and work together with actual communication, but the online component is cool and it works.
The notes are pretty interesting, and they've helped me before - stuff like "treasure this way" or particularly "beware ambush ahead" or "trap ahead" are life savers. Same with the Bloodstains.
It's cool to see how someone died, but I don't click on notes and bloodstains all the time. There appearance more so just serves as a sort of warning in general - be cautious and keep your eyes open.
Basically you can be a human or a soul while you're playing. But mostly you'll be a soul. As a soul you just have less HP, and can allow yourself to be summoned to other players games, while as a human you have more HP and can then summon those players who are souls in to joining your game and helping you out.
Helping someone defeat a demon when you're a soul gets you lots of souls (basically the ingame currency used to do everything) but it also restores you to your human form.
And I've found when in human form I'm more than willing to bring other friendly souls in to my world to assist me. It's just win win for everyone when they work together.
As a soul in another players world it doesn't appear that you can advance your own progress in your game though.
That is to say, I was summoned to another player's game and helped him defeat the Tower Knight Demon. But, when I was sent back to my world, I found the Tower Knight still existed in mine, so I, now in human form, summoned two other souls to help me in my game and together we defeated the tower knight. I was able to progress me game then, and those players reaped the rewards of defeating a demon.
You asked about the combat earlier - I like it.
I'd describe it as more tactical than hack 'n slash.
You won't be mowing down hordes of demons ala Gauntlet or Diablo. Instead each fight seems up close and personal. It's fun too.
Basically you have an endurance meter which dictates how many actions you can do. Swing your sword and your endurance meter drops. Sprint, and your endurance meter drops. When you have no endurance you can't do anything.
Granted it automatically starts to refill when you stop taking actions but in the thick of things you have to be careful.
What I like is how blocking works. A shield can block 100 percent of damage - instead of taking damage you lose endurance. So block a hit, lose endurance. Block too many hits in a row though and you'll have no endurance and be able to neither block or attack.
Also, when you have your shield up and readied your endurance meter refills slowly.
So you have to maintain a careful balance between offense and defense. You can lock on to enemies and do some other defensive moves such as rolling away or hopping back.
You also have some options to counter attacks. You can hit L2 at the moment an enemy strikes and deflect it and then follow up with a counter attack.
I tend to straight up block, rather than parry and counter attack.
My character is the Temple Knight which is basically a Paladin type character - I use melee weapons and can cast "Miracles" which are basically healing/status effect removing spells.
That said, once you gain the ability to upgrade your stats you can build your character in to any shape you want. You aren't shoehorned in to a particular style, nor are you limited to certain types of equipment.
Oh, and you'll die a lot. In fact, you'll die in the tutorial
Even a basic enemy can take you out in a couple hits.
It doesn't feel cheap though, at least not so far. You just have to be cautious, careful, and not be easily frustrated.