Well, nothing but:

- A MUCH, MUCH more convenient setup all in one

- The above mentioned setup being nearly 10gb smaller while still having all the content

- Some change in the scripts here and there, probably minor optimization that however make some mods incompatible goty with non goty edition

- Due to mentioned modification above, most new mods are NOT gonna get compatible for both goty and non goty, giving the goty edition a significant longer longevity mods wise

The difference between goty and non goty script is mentioned in some mods on nexus, so the differences exist, even if someone that there is no need to name, continue to deny it

If all of this is not enough, buying the goty edition cost less then base game + exp, so if you already have base game and want the exp, you WILL pay more for absolutely no reason at all, adding that on steam the exp was discounted at least once, but never here on gog

Content is pretty much identical, most bugs too

So yes, the bloody same....right