Seriously this mod is amazing as I'm sure many others have said. I sort of like the idea of playing the game in the state it was when it came out before using any mods. But the old resolution of 320 X 400 or whatever it is, really hurts my eyes lol.

I can play Vanilla Duke Nukem easy enough though.

Probably the only reason is nostalgia, provided you run it slow enough to not cause the bugs to crop up.

With DXX-Rebirth you can play it vanilla style with none of the lighting effects or anything, should you want to do so, and you don't have to enable any of the gameplay changes unless you want to (they are off by default and that's how I've left them).

Have to say, I'm loving the DXX-Rebirth mod.

What game play changes does it make.

None that I know of besides fixing bugs that were present in the original game.

Since 0.54 (or something like that) there has been some homer code that made homers fly differently than the originals (although truthfully the only people who noticed it were Ranger pilots at a level that I will only ever hope to achieve). The new homer code has been written to correct that and will be implemented in 0.58.2 (or possibly 0.59.0 if there's not a 58.2)

Other than that, everything is either exactly the same or exactly how it SHOULD have been (for instance, there were many FPS-dependent things, that have been converted to work the same no matter what FPS you're at).

So truthfully, unless you just really LIKE 320x240 resolutions and old buggy gameplay, there's really no reason to NOT use Rebirth :)

Very small ones indeed. When using D1X-Rebirth go to the Options -> Misc Options page. I leave these options as they by default, but you can change some of these options if you wish.

Persistent Debris (off by default)
No Redundant Pickup Messages (off by default)
Show D2-Style Prox. Bomb Gauge (on by default)
Free Flight Controls in Automap (off by default)
No Weapon Autoselect When Firing (off by default)
Only Cycle Autoselect Weapons (off by default)

You can also customize which weapons you can cycle through and the order that they cycle.

Oh right but nothing dramatic like the eduke mods or the system shock 2 mods

Nothing dramatic. The aim of the DXX-Rebirth ports are to be as true to the originals as they can, so only bug fixes and those very minor changes. I don't even think they want to have higher definition textures other than the briefing screens (and possibly the cockpit HUD), so for graphics it will just be an increase in screen resolution with some AA and AF if you wish, to smooth things out a bit.

The only reason to play the original version over a source port is if you're using a very old computer.

If you play with a SpaceOrb 360 you need to play with the original version, though you can play in highres which Descent supports.