OMP stands for OldUnreal Multimedia Patch, if I'm not mistaken .You can find it on the OldUnreal website too. It's a pack of some additional renderers and audio drivers, which are outdated by the 227 ones. Still, as Kentie's renderer doesn't work with this patch, I'm relying on the OMP for better sound (in OpenAL). If you want to try this combination you should go for OMP 0.2 installer for Unreal Gold. OpenAL may give an error at start but reinstalling it or applying a more recent version should do it. Compared to the original sound driver, it's less buggy, and has nice reverb sounds.
As to the DX9 renderer, I remember having tried this one some time ago, but I quickly went to OpenGL. I don't exactly remeber why, other than the fact that OpenGL simply seemed more complete. Kentie's DX10 renderer, to me, has the advantage of looking more like the originally intended 3Dfx Glide look, while allowing for high resolutions, and Glide-like effects, as I said. DX9 and OpenGL definitely miss the point on some maps (mostly Dark Arena though). I'm currently in the last third of the game, and I'm really surprised to see the difference. Just have a look at Kentie's DX10 page, scroll down a bit and you'll find a comparison screenshot about multi-pass texturing on the sky. What you're missing in non-glide looking renderers is better day-night cycle (slightly, because of the better blended skies), and a darker alien atmosphere, so it's quite subtle a change overall. Having a dark sky also feels more coherent with the ground map too (again, Dark Arena and another village map). However, DX10 has some bugs here and there (small ones though), and I think OpenGL still looks really great, mainly when you activate all the 227 patch video options, which give a more modern look and makes you forget a bit about the odd bright skies and very reflective floors.
So... tradeoffs everywhere. I'm really enjoying the game with an "enhanced original look' with Kentie's, but OpenGL + 227 (you can skip DX9 for this one really), while it seems less faithful to the 1998 Glide look, really enhances the game. You could also simply choose Glide (gog provides nGlide for emulation), add the OMP for better sound, and play a with this. I've noticed that the Dark Arena sky is definitely changed by the 227 even in Glide, but overall, the game is great whatever the renderer and patch.
Edit: by the end of the game, Kentie's renderer was far less convincing on my PC, as I had quite a lot of "blank/black" texture bugs in the dark, foggy levels. Maybe it's just something with my PC though.
Edit 2: corrections after skipping to some key maps with OpenGL and 227.
Post edited December 04, 2013 by Darucas