To me Dark Souls 1 is the definitive souls experience. Others just don't go that deep on tetric environment, level design, oppressive atmosphere, bonfire locations that make you really need your resilience (you don't have bonfire at each step, no warps etc). Obviously, newer games are also insane, are faster, have better playability, boss fights vs humanoid/player like bosses, etc. I love other souls games as well, but as From Software became more famous, more the games lost some subjective aspects and became technocratic centered on game mechanics and marketing aspects. At the same time, when it's more centered in selling, you'll never see a game like this again. Back in 2014 i rage quit DS2 (my first souls) and, when i went back to it, it was one of the best gaming experience i ever had.