Right now I decided to run Quake 2 in software mode for a bit. Holy crap! It looks way better. Sure it's pixiladed but it looks really cool and the gore looks quite horrific. You can see all sorts of nasty little details.

I'd still recommend not to use software mode as you will lose colored lighting. Even using OpenGL you can still disable texture filtering, etc., making it look all "retro". That's what I did using this as my autoexec.cfg: It's basically the best of both worlds. Crisp, pixelated textures, yet atmospheric colored and dynamic lighting.

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I'm using Yamagi Quake 2, by the way, which to my knowledge doesn't change anything about the visuals. As far as I know these commands should work with vanilla quake too, though.

Do you add those lines yourself?

I'm sorry, I don't understand. Do you mean where you have to enter these commands? If so, you just need to create a new text-file in your baseq2 folder (for example C:\GOG Games\Quake II\baseq2), copy all the commands into it and then rename the file to autoexec.cfg. This way, whenever you start Quake 2, all those commands will be activated automatically.

Beware though, if I recall correctly your previous values will be overwritten once you've started the game. So, if you first want to test these commands without losing your own configuration, you may want to backup your config.cfg file first (With Yamagi that can be found in C:\Users\USERNAME\Documents\YamagiQ2\baseq2, with vanilla Quake 2 it might be in the normal baseq2 folder).

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Here are some screenshots to show what the game looks like using Yamagi and this autoexec at 1920x1080:
http://i.imgsafe.org/c77a5973df.jpg
http://i.imgsafe.org/c77ccb6aed.jpg
http://i.imgsafe.org/c77e2f0957.jpg

I often try to play older games at lower resolutions, but in this case I was very happy with the result at this resolution.