If you already have DS1, you probably want to use dsfix instead of spending the extra money.
I suppose this is a great version for new players or console players to get into the game.

Dark Souls 1 will remain one of my favourite games of all time.

Does it run better?
Not necessarily, there is a certain fluffy boss which ate at my FPS, as well as some fiery bosses.
I might just have gotten too used to a dsfixed DS1 though.

Does it look better?
Yes, no doubt about that.

Does it sound better?
I am not noticing any obvious audio improvements.

Does it play better?
Honestly not, some areas will have you stub your toe on a pebble and will require a running speed to cross them.

I would recommend it, especially if you have never played through Dark Souls before.
There is no real point to buy it if you have played through the first one, except if you love the game and wish to play a somewhat prettier version of it.