Steam DF graphics look almost exactly like the graphics mod I used when I played DF before it went Steam. I literally couldn't tell the difference upon release.
They did make quite a bit of the UI better, yes. While I do use keyboard shortcuts for lots of things still in the Steam version, you no longer have to things and can just use the mouse.
Also a bunch of things that were just completely 100% unusable without DwarfTherapist are bearable now.
I don't remember many specifics tho. It's been a while and I checked yesterday and it seems I don't even have the old folder anywhere any longer.
Oh and DFHack of course. That's still something you want that automates a bunch of things you really don't want to live with otherwise.