Yeah. Dark Souls 'as released' was limited to 30fps and was upscaled from 720p. Durante's DSFix patch nearly sorted it out; there was a couple of ladders that you needed to switch it off for, otherwise you'd fall through the world, and some rolling over logs in Blighttown was a bit dodgy. Otherwise, completely playable and graphically good.
Remastered fixes that; the flame effect on torches is different, and the framerate is a bit more stable when it could be dodgy before. (Fighting Sif, for some reason.) It doesn't redo all the rushed sections after Sumo + Stringbean to match the concept art, so Izalith and the Tomb of G's are just as 'good' as ever, and Gwyn is still stupidly weak to parrying and magic.
If you've never played Dark Souls 1, then obviously this is the version to buy, but still unreasonably pricy for its age. The first 3/4 of this game is DS perfection. DS3 is the most polished and has the best bosses; DS2 has the best DLC and multiplayer, and I find it the most fun to replay as so many builds are viable. DS1 has the best world design and atmosphere by far, though.