Canon Welding: It's fairly obvious that The Eternal Game wasn't originally supposed to be set in the same world as the rest of the Xaterex Storyline.
Hilarious in Hindsight: According to the author, he didn't actually have any idea that The Hunger Games existed until midway through The Eternal Game. After that, though, The Eternal Game and the third part of The Shadows Coil do take inspiration from The Hunger Games series, so obviously he read it at some point.
It Gets Better: Pretty inevitable for a series that was over five years of work long. According to Word Of God, the original version of The Eternal Game was written in 2007 (which accounts for the extremely poor beginning section), and the revised version in early 2010 (The ending few chapters are marginally better). The fanfic's author has stated multiple times that the earlier volumes in the series are much worse in comparison to the final four, an opinion shared by the majority of the fandom.
So much so that apparently a rewrite of The Eternal Game has been planned, to make it fit with the rest of the series.
To sum it all up, the original volume (Into the Darkness was written when Varkanax39 didn't really believe anyone would pay attention to the saga. The Eternal Game was written as a completely independent volume, but eventually the author decided to weld the two series together into one, which was done in The Shadows Coil.