I played Dark souls 1 and Dark souls 3 before Ds2:SotFS, and even with that ds2 is my favorite. Its challenging but never really gets really frustrating like the others, the game performs beautifully, and I love the freedom offered by things like the soul vessels.
I also like how you get some choices on where to go first at some points, mainly in the beginning and at the memory sequence part.
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I personally found that Dark Souls 2 was too easy to complete and my first playthrough is always solo, the main thing i liked about it was the twinblades, they added a new style of attacking where you could set your own style of using the weapons.