Yes, there is an actual download, and yes, this patch does change more than just details in levels.

The Jazz Jackrabbit 3D Enhancement Patch is supposed to fix most of the game's problems and revive some of it's unfinished parts. On top of that, it does some important design changes and adds greater level of detail to not only the levels, but also the gameplay and overall look.

NOTE:
1.3 is the final release of this patch. I won't work on more of these, but everyone is free to edit and improve on top of my work! You can distribute this anywhere and anyhow you like (My content, that is, not Jazz3D itself), but please do credit me.

Screenshots (Click to enlarge):


More:
http://i40.tinypic.com/2qc1s1y.png

Videos:
Early Alpha of v1.2
New camera in the upcoming 1.3 release

Changed (Short list):
* Improved camera control.
* Improved controls.
* Better physics.
* Improved Graphics.
* Heavily updated main menu.
* Greater level of detail in many of the maps.
* Higher difficulty.
* A long list of bugfixes.
* More balanced gameplay (Still working on this though).
* Xbox 360 controller support

The complete lists of changes and to-dos are included in the ReadMe.txt file!

The package also includes a new map called "Q.unr"
To load this map, open the Console with "~" (Tilde) and type "open q" (Or q.unr).
The Q map is a test map I created for testing various gameplay features. You can test a lot of those there, if you want to!

Downloads::
V 1.3c

Old Unsupported versions:
V 1.2
V 1.1B
V 1.1
V 1.0

** How to install (In case if someone had any problems with this.):
Extract the package in your game directory and replace all the files (If it doesn't ask you if you want to replace them, you're doing it wrong). Yes, that's it. =)

If you come across problems in this patch (And you will), please let me know about any of them, because if by some chance i missed those, I may fix them.

I also accept criticism, so don't hesitate to speak your thoughts!

Thank you and enjoy!