It's A Total Conversion
...so you don't need Duke3D to play it. I just gave it a short try. It has large outdoor areas and you can free other heroes who will then fight for you. You also got special powers, some sort of magic that you can activate after killing enough monsters.
Basically the story is that you're in a medieval world after a warp accident and some mysterious dude asks you to kill some ugly monsters before he'll send you back home to your dimension.
If you enjoy Tronyn's maps you'll really like this
I'm seeing a lot of Quake textures there... I'm wondering why he did a TC for Duke and not from Quake from start....