Apart from better visual quality (although the clearness can detract from some of the original textures), multiplayer allows for more people at the same time (coop and PvP), covenants can be changed on bonfires instead of having to go to the covenant leaders, there is one additional bonfire close to Vamos that wasn't in the original, and you can pop multiple items in bundles (souls and humanity) instead of individually.
Other thing I noticed which I don't know if it's a change though is that when I defeated Mildred in Blightown last time I was given 2 Estus which were not dye to someone kindling the bonfire: there wasn't the noise you get then and it happened just instantly. Had that happened to anyone else? Sounds like when you defeat an invader in DS3, but haven't played it and can't confirm it.
Anything related to Dark Souls!