Iain: Issue with black / missing / blocky textures was that the game uses a 24 bit frame buffer which is no longer supported in latest drivers for Nvidia and ATI cards. GOG have fixed this though and it looks amazing. Running with everything maxxed out and 1920x1080 resolution, the city is vibrant and alive. I could never run it in this way back in the day having to knock settings back to get it to run, it was a system hog back then!
No it's not. It's an ati zbuffer issue, that they aren't interested in fixing because it only effects the older dx interfaces, and only when the zbuffer is used in a specific sort of way. Crimson skies and one of the mechwarrior games (3, iirc) are affected by the same bug.
Tiax: Is it possible to choose 32-bits color ? I read you can only select 16-bits, dunno if the original game had this limitation.
32 bit colour support is added by GOG's patch, and is on by default. (Aside from when active subtitles are present on the screen, iirc, when it'll drop back to 16 for a few seconds.)
Nirth: How's the performance? With my old physical copy I found it's rather unplayable as soon as you enter 'inventory mode', I can't move items and I think the game will freeze if I stay to long in it.
Also fixed by the GOG patch, albeit at the cost of the static effect on some menus. (There's a config option you can use to turn it back on if you want to see it, and you happen to like slideshows.)