The game itself is said to be best described as a free-to-play coorperative third-person shooter with a fort building theme that takes advantage of the day and night cycles while you try and fend off waves of enemy attacks.
The game is said to use a RPG style progressions system with a number of other familiar elements from the RPG world like looting, PvP battles, and multiple campaigns are all apart of Fortnight. The game has apparently evolved a lot since Cliff Blezinski, Mike Capps, and Rod Fergusson where at Epic.
Epic is taking sign-ups by those who want to be part of testing and playing the Alpha version here.