I'm looking for a great port thingy
IT should have/support the following features:

* Fully working Coop SP campaign - Most important since I wish to play with my brother.
* Windows 8 (or 8.1) 64-bit OS - Both my brother and I have this infamous system.
* High Res textures - The old textures of the game, while nostalgia is great, I would like something more... detailed.
* Music of the game mattes not... - yeah... that.
* "Mostly" classic game play... nothing completely mind blowing new.

I haven't tried the following Q2 ports, but these are the ones I found.
I would like to know from people which one I should try.

r1q2 _ http://old.r1ch.net/stuff/r1q2/
Quake 2 XP _ http://quake2xp.sourceforge.net/
KMQuake 2 _ http://www.markshan.com/knightmare/
Q2PRO _ http://skuller.net/q2pro/

Those are a few of the ones i came across the seemed most promising, But i don't know which i should use.
After all, it needs to support the above...
we are looking for a classic Q2 play through,
but with an "engine" optimized for systems today and a better appearance for the game.

Berserker is probably the best looking one, don't know about coop http://www.moddb.com/mods/berserkerquake2

I don't know about co-op, or if it high-res enough for your needs, but I used to use Yamagi Quake. I played it recently and it worked fine. Don't know about Win 8 binaries, but if you have a friend who owns the latest VS Studio you might ask him to compile it for you.

Anyway, there is high possibility XP/Vista/7 binaries will work just fine. Especially later two. :)