Doom3 is such a fucking terrible mess, it hurts. For a start there are three projects to choose from:
ioDoom3 - https://github.com/iodoom/iod3
Literally fucking nothing, a complete false start with zero work done, not even 64bit port, pathetic.
dhewm3 - https://github.com/dhewm/dhewm3
Updated but completely breaks compatibility with the SDK and thus existing soft mods. In particular the mods that made the game look half way decent like sikkmod and dentons's enhanced doom. What's more a complete lack of interest in implementing comparable advanced graphics features of their own.
RBDoom3BFG - https://github.com/RobertBeckebans/RBDOOM-3-BFG
A fork of the updated Doom3 release. All the added engine features are a pile of fucking crap that just make the game brighter. It also cannot be played online without Steam, yuck. Robert has added new shadow rendering which is cool. However they also completely couldn't give a fuck about maintaining compatibility with mods, they fuck with settings without a care for compatibility.
What really fucking kills me is that users are better off with an original version of the game with soft mods like sikkmod and a texture pack. It's like all this work has just been to make doom3 worse.
It's not fucking rocket science. All you need is a port with:
Backwards SDK compatibility