Does anything get added other than "improved" graphics?

It depends what platform you're asking about. If you're asking about consoles, then you get the capability to mod the game. If you're asking about the PC version, you get an upgraded 64-bit, DirectX 11 engine.

For PC? 64-bit exe, DX11-support, other smaller and less obvious improvements, etc.

If you mean new content, gameplay features or something like that, then the answer is a huge "no".

Im on PC, what about gameplay, any new quests or?

No. It is a remaster, not a remake.