I never got the complaint about OG Deus Ex feeling "clunky" when movement feels much better than HR and you get freedom to use augs whenever you want instead of just contextual bullshit.
Some aspects of the game are clunky, but that is absolutely trumped by the general intelligent design across the board you won't get from modern garbage.
For movement in particular:
The headbobbing is primitive.
There is no running animation, moving around feels like you're a robot with gyroscopic stability. Even Doom had a running anim.
Jumping makes a "Hmph" sound effect every time.
The default concrete footstep sound effect sounds like JC wears clog shoes.
There is no feedback when landing from height.
All of these things are addressed by GMDX:
v9.0 in development adds a nice (optional) new headbobbing effect.
Running animation is available in v8 and adds a natural feel to movement.
Jumping sound effect plays with a 33% chance per jump.
GMDX adds five new groups of footstep sounds, and the "clog" sound effect is no longer the default sound effect and only plays for a narrower texture group.
New audio and camera effects when landing from height feel great.
There's other things too, yet it's all window dressing. Important nonetheless, and a big improvement to how the game feels, but a lack of these things is not a good enough reason to put the game down. At all.