I have played Andean Abyss, Cuba Libre, A Distant Plain, Falling Skies, and Fire in the Lake. FitL is easily my favorite. I enjoy the complexity of the interactions between the two loosely-allied sides, but the tension with their differing victory conditions. But mostly I enjoy and appreciate the maneuver element of the forces, as the map plays more than any other like a wargame. The "maneuver" on ADP is too constrained, Cuba Libre is like a knife fight in a phone booth, but FitL allows for many more options.
One complaint I have about the COIN system is that, at least in our group, anyone can win. Once you get near the victory conditions you get beat down by the others, and someone else becomes the king, until they get beat down. It seems to be more about lucky timing on that last Propaganda Card. For example, in our last game of ADP, I would have taken the lead (and met my victory conditions) on the next card, but a PROPAGANDA card was revealed. So I didn't win. And in practically every one of our games, someone has been within a card or Propaganda/Election/&c. of winning, but ended up not winning (and often pummeled down to the bottom). While this makes for tension and drama--and even fun--I don't know if it actually rewards good play or a viable strategy.