I just finished playing all three versions of UT for hours tonight. I've never played the original before tonight because I didn't start playing UT until 2004. Honestly, I can easily see why some of you dislike UT2004's mechanics. This is coming from a guy that did nothing but play UT2004 almost every day for a very long time. Here's my take:
I'd like the original UT pace with a slightly higher jump, a wall dodge that has the same momentum as the standard dodge, and an option to jump normally with jump boots equipped. I'd also like to include ramp boosting, lift jumping, and all the other tricks. I'd remove all dodge jumping and double jumping all together. With a higher default jump and a wall dodge that gives you the same angle and momentum of a standard dodge it should be acrobatic enough for most players.
The original UT is the only one that felt natural, while UT2004 felt like I was floating, and UT3 felt like I was 500lbs overweight every time I left the ground. I haven't touched a UT game since 2008 and these were my reactions from playing each over and over again for a side by side comparison on a DM-Deck map for a sense of similarity.