Originally, it was to cash in on TWDs popularity with another zombie show during the long off-season. It is original and not connected to any comic book.
It was supposed to cover "the beginning" of the apocalypse, but did not do this very well. The characters were not, (and still not), as likable. I dropped off watching as well. I picked it up again for season 3 which was not half bad, (actually better than the last couple of seasons of TWD).
TWD is currently about 2-3 years into the apocalypse, while FTWD is supposedly still in the first few months.
TWD is set in the southeast US, while Fear started in LA, went into Mexico, and still in that southwest desert area. Too far apart to be connected, however there is supposed to be a "cross-over" with at least one character.