To be honoust I don't know very much about it, other than the distance and vertical meters: 500 km and 10.000 meters.
I chose it mainly because it was close to home (I live in The Netherlands). Also, I liked the fact that this is a proper mountainbike race and not the more common gravel'ish track. Other than that I am pretty much in the blind on what to expect. Which is part of the fun I guess.