I have the game on CD already, but I have a few 3D issues with it. Are there any improvements in the GOG version that will make it run better, or am I basically just downloading exactly what's on the disc?

Edit: I'm an idiot. I didn't realize the D3 note in your topic title, haha. I started going on and on about Descent 1's compatibility issues with XP and Vista... I don't have an answer to this question. I own the game and don't intend on buying this one.

I have run D3 on XP before with no issue at all. However, I haven't tried it with my latest video card so I couldn't tell you. I just bought D1/D2 off here so I'm going to install D3 off my disc tonight and see how it plays. I'll post back here and let you know.

True, D3 does work on XP, I had a hard time installing on a Vista machine. Also, the newer DX10 graphics cards do occasionally throw a wobbly. The best settings I found used OpenGL (which are occasionally buggy).
I look forward to testing GoG's version out.