Actually, I cancelled my Mumak and my Attack Troll...each for different reasons.
Although I believe that the Mumak sculpt is indeed excellent and exceedingly detailed, I really have a problem with adding more dead or dying sculpts. I already own Sideshow's excellent Santi with Bomb piece, as well the Haradrim soldier figure. That is enough fatalism for me.
As for the Attack Troll, I already own the classic Cave Troll, and once you own that piece, there really is no need for another troll. In short, the first Cave Troll set the standard for the character...the new piece is much like the second Balrog. It has been released for those who missed the first go-round.
I am still on the fence concerning the last two horse and rider pieces...Gimli/Legolas on Arod & Aragorn at the Black Gate. I don't think I will preorder these, but I might pick one up on Ebay if the price is right.
As far as I'm concerned, my final must-buy LOTR pieces will be:
King of the Dead
Pippin
Lady Galadriel
Sauron
Peter Jackson as Corsair
...sailing off into the West.
B.