Full disclosure, I never purchased the Steam version, I played the SNES rom. This is partly because the game on Steam came out shortly after I beat the SNES version. So all the things here are from research not experience.

As one might expect, it isn't a true port, it's the port of the iOS version, which is fancy sprites overlaid on a base cartridge of the GBA ROM, which is the rewritten version of Final Fantasy VI. It fixes the bugs, most notably the "Sketch" command which caused the SNES ROM (and presumably the PS1 port) to crash but also presented itself with some unique problems (a butchered soundtrack)

So here's some rundown to make it play the way one would want...

* It does NOT have the cutscenes added in the PlayStation version.
* I've heard that it does have the GBA music but that can be replaced via patch
* A project to replace the SNES mods was underway as of last year but has gotten held up. As of January 2017, the admin is still active. [http://steamcommunity.com/groups/ff-modding/discussions/10/451]
* It does censor the "Celes torture scene", however, that can be fixed with a patch that was released for the GBA version. [http://steamcommunity.com/groups/ff-modding/discussions/10/451850849200543624/]
* Mods to remove the bilinear filters and tone down some of the awful sprites (like removing male characters' guts) are available
* It is possible to change the font. While "FFVI Explorer" helps access files, there is no known mod to automatically replace the font to the original font.

Overall, there is much to do, but remember, FFVII had a lot of problems too that took years to fix.