I've written a good deal about Missing, going so far as to translate four volumes of the series for Tokyopop's ill fated novel line.
The first two volumes - the only two ever published in English - are nice stand alone volumes that skillfully blend J-horror tropes with actual research into folklore and the occult.
Then an arc plot enters the picture, and volumes three through eight are absolutely fantastic stuff.
I finally finished the series a few minutes ago, and I regret to inform you it ends with a limp flop.
After volume eight he clearly makes a conscious decision to head for an ending. Instead of being carried along by a wave of good ideas, he methodically attempts to manipulate his already dangerously immobile characters into the positions he has decided they should be.
One of the more obviously flaws throughout the series was the somewhat shallow characterization, and the obvious inertia all these characters present when attempting to give them arcs, or get the plot moving; each of them is essentially complete and has nothing built into their being that makes them actually do anything proactively.
It takes him five volumes to force them into place. The result is simply tedious. And the places he forces them into are frequently simply not that interesting or satisfying; he gives you a plot element you knew was coming, and zero payoff on it, so you're left wishing he hadn't bothered.