The steam version works for me, straight from digital download. Even runs well in HD. But as always your results may vary. I don't have any experience with the GoG version.
btw, JakePlisskenSDA, I didn't know you were into SS2? Well, makes sense actually. Same engine as Thief II.
Yep, I run any% but haven't streamed it/posted a PB yet. Waiting for sub 14 in practice before I think I'll feel confident enough since it's so fast paced. I'm also trying to learn Space Botany's All Modules glitchless impossible route.
I have been very busy with Postal 2 and Redux lately, but I'm starting to get into SS2 and Thief 2 again. Have the entire route down currently, but not yet consistent enough to do a proper run.
SS2 has gotten a patch on 9/29, with a few bug fixes, including one involving some conflicts between SS2, the Steam Overlay and Windows 10. It should be pretty stable by this point.