Finished it today. The long wait for the release was well worth it! There is some excellent level design here. In the main game you visit the labs and industrial areas of Mars City, but here you can see where the colonists actually live and work. There are living quarters, malls, hospitals, recreational areas... though you added a lot of new stuff it feels right in place, as part of the Doom 3 universe. Some really memorable architecture: the mall atrium, the office complex, the Y-bridge room. Sometimes the architecture looks more stylish and memorable then what you see in the main game.
Really liked the more non-linear parts, but you could have added more alternative routes when you give the player an objective. For example, when the player needs to find that bridge only to see it is broken, you let him backtrack exactly the same way. This is a missed opportunity for creating an alternate route and giving the player more choice. Most times non-linearity just came from looping layouts and some dead-ends branching off. But it's more non-linear than what we see normally in custom levels, so I am not really complaining.
Faster run speed, no stamina and better shotgun are very welcome additions to the gameplay. Apart from that it stays very true to the Doom 3 formula, and since I like Doom 3 I also like this.
The only part I didn't like was that unbalanced massive monster attack where you first pick up the shotgun. Others already mentioned it above in this thread. I was only armed with a pistol, a freshly picked up shotgun with 4 shells and the grabber and had to fight of imps and heavily armed Zsecs while the melee zombies pretty much prevented evasion. I died a dozen times and it was pure trial and error to survive this part. After that all the follwoing fights were okay, much more balanced.
So after all this years, you got this first major release of your project done! I hope you have a party to celebrate it!