Is there a mod for Doom 3 that emulates Doom 2?

Solution 1:

I know this post is quite old, but your best option is to use Doomsday Engine, it adds all the feature that you are looking for 3d models, better lighting, TCP/IP support for networking and the very needed mouse-look support.

If you are looking to play Doom 1 or Doom 2. This is what I would recommend anytime you got some nostalgia.

Screenshot of the engine below:

Solution 2:

There's Doom II wad for Doom 3 which you can get from DoomWad Station.

You might also want to check out Doomsday mod, which isn't specifically for D3 engine, but still adds much better graphics and sound to a classic game.