I'll be the first one to say that Doom 3 wasn't very good, mostly because it threw away everything that made the classics so great in favor of half-assed horror elements, but its still heartwarming to see someone this passionate about bringing Doom 3 in to the modern era.

The mod in question is Doom 3: Redux, a solo developed project that boasts improvements to the visuals and audio design, new game modes, restored content, new features, but most importantly, no changes to the overall spirit of Doom 3. If you're wondering how exactly this looks in action, here's a rather lengthy trailer:

And if you can't be bothered to watch the video, here's a small image showcasing the difference between the original textures and the ones you might find in Doom 3: Redux:

The center image is from a community texture pack Doom 3: Redux is based upon

The currently available version is nearly feature complete, with only a couple of audio-logs still being worked on, but due to the limited amount of people beta testing the mod you may encounter some bugs. From what I've seen others complain about there seems to be a bug where lights flicker for no reason, the menus are occasional unresponsive, and extremely large resolutions can run in to legibility issues when it comes to text, but other than that there really isn't much negativity about the mod.

Do keep in mind, however, that Doom 3: Redux works only on the standard version of Doom 3, and not the BFG edition, so make sure to install this on either a retail, or Steam copy.

On a somewhat unrelated note, the latest Doom is currently in an open beta phase, so if you would like to see how the Doom series has evolved (or devolved) give it a spin, its free on Steam.