I think Something Awful's thread on the game did a great deal to help the game reach other regions, importers practically saved it (Or at least ensured publishers would release the game elsewhere when Sony didn't want to).
It was such a refreshing experience to play, from the way combat matter every step of the way, and of course it revolutionised multiplayer. I remember at the time people were so confused as to what the multiplayer system actually meant, but over a decade on it's a common feature in a lot of games (Or at least in Soulslike games unless I'm mistaken).
The atmosphere was pitch perfect too, and I felt Dark Souls kinda lacked a little bit in comparison. Valley Of Defilement and Latria were the absolute best stages for this, the team put a lot of effort to making the disease ridden regions and oppressive prison just plain work. It's horror that isn't too scary to drive people like me away, but it pulls me in instead, and I vastly prefer that over jumpscares.
Demon's Souls is a legendary game, and if/when a remake is made I hope it reaches more people who missed out the first time.