Okay, our orders are way different right now. For me, it's
1) Dark Souls
2) Demon's Souls
3) Bloodborne
4) Dark Souls 3
5) Dark Souls 2.
I disagree somewhat about the game having a nice mix though. I feel like shields just get you killed in this game and you should really just roll instead. The problem is there are so many enemies in most areas that having a shield up is just a liability because you're going to lose all of your stamina.
I had a lot more success just playing the game like Bloodborne and two handing a strength weapon with fuck all armour and a steady dodge finger.
I feel like DS1 is cool all the way through (apart from the Valley of Defilement which can fuck right off. Also, the treck to the last boss is bullshit), and has some of my favourite level design in the series. I am just a sucker for levels with one checkpoint that weave their way back to the start.
I know I spent a lot of time getting lost in the swamp. I don't think I spent that much time on multiplayer though. I'm guessing you uncovered all the secret areas because you've mentioned 2 and you can't get to one of them without another you haven't mentioned. I did die a lot to a boss that you haven't mentioned and might not be up to - he's optional and one of the best fights in the series, even if the camera is a tougher foe than he (seriously, breaking lock if the camera moves slightly above you is bullshit.)
With the magic thing, they fixed it in DS2, and all they really had to do is follow that formula.