TL;DR
DX models be jank. We try to fix.
The problems
While the human models in Deus Ex generally look great in their own strange way, we modders run into some hard limitations when trying to use them for anything other than what was initially intended.
Lack of animations
Not all characters have all animations. Particularly females and larger people got the short end of the stick when it comes to combat, as two-handed weapons are flat out not supported. Equip a maid with a LAW and take a shot at her, she'll just stand there like a lemon.
The trench coat guys can do most things, like crouched walking (which is exclusive to them), but they can't dance.
Some animations are completely missing, like strafing in different directions. If NPCs are running and firing, there's a good chance they'll be moonrunning.
Sausage fest
Women are generally underrepresented in Deus Ex, limited to generic civilians outside a few exceptions like the WiBs, Jordan Shea and Anna Navarre. There is only one model with flat shoes, the rest have high heels. There are also no female children, and no black adult females. Since they fixed most of this in IW, I think we can safely assume it was an oversight.
Strange proportions
As you may notice in the above image, all humans have excessively long legs and small torsos, the women in particular. The only justification I can think of is accommodating low resolution CRT monitors, the long legs making it easier to read a walk cycle from far away. That still doesn't explain the difference in genders, but it's the best I've got. Apart from the legs, everyone also has tiny heads, but that's common even today.
Modern screens
When I said the models generally look great, I meant it with one caveat: On the low resolution CRT monitors they were originally intended for. The 128x128 textures and 300 vertex models got smudged on the screen, and players were left to fill in the blanks with their imaginations. This created a neat illusion and was a big part of what made Deus Ex visually compelling. On modern flat panel displays, it's a very different story.
Our solutions
To fix all this, we had to rebuild everything from scratch. Unreal Engine 1 doesn't have a skeletal animation system, so we couldn't reuse the original animations.
New animations
The work ended up being a mix of tracing from the originals and entirely custom work. This was carried out by AnasB and myself.
Better models
When creating the new animations, it became clear early on that we were working with something very different than the original animators were. I haven't been able to confirm this, but it seems to me that they moved each vertex by hand instead of using armatures. When the classic models are animated using modern techniques, they end up like this:
So we had to add more vertices to allow for better deformations:
But more vertices isn't just more vertices. We had to completely rearrange them to make the deformation work. This is called retopology, and it's basically about making sure the models mainly consist of polygons with 4 vertices, and that the vertices are as equidistant as possible.
This work also improved lighting on character faces, smoothing everything out and preventing those diamond shapes that would often appear.
New animations
I also added some extra animations for expanded gameplay and flavour. We've got support for a simple cover system without weapons.
We also have much more expressive faces now
More females
I've added two new female models, a child and a jumpsuit. I've also given the trench coat ladies flat shoes and longer coats, so they're more versatile.
General improvements
I've fixed the odd proportions and added more detail where I felt it would improve things without adding more polygons than necessary, or stray too far from the original design.
New Blender addon
Skywolf285's Blender addon has been the go-to solution for working with UE1 models in Blender, but has not been maintained for a long time, and only provides basic functionality. I decided to fork it, so it would accommodate Deus Ex a lot better. Now every export operation is just a single click away, and everything UE1 needs to know about the mesh can be set up in Blender itself.
Conclusion
This work was slow and extremely laborious, I made many mistakes and had to redo things from scratch several times. We're not done yet, there are still adjustments to be made, more flavour animation to add etc., but we've reached a point that it's all usable and has surpassed the original animations in terms of features.
Thanks so much to AnasB who helped me get started with his traced animations, and to the entire Machine God team and other modders for providing feedback and advice up until now!
All of this work is available here, feel free to use it however you want.