Another very good review.
I really like the armour but I'm not a huge fan of how the smaller members of the force are posed, especially when you see them next to the Behemoth which shows just how much movement and character you can get out of a model even in a bulky suit of very heavy armour.
I'm quite a fan of russian/soviet tanks so I can echo a lot of your comments on the armour from the plane perspective, it looks very military and functional, designed to do a job and do it well.
I can think of a few uses for the Behemoth in addition to the Mercs game, from a heavily armed AE Bounty character, to a power suited hero or villian for a superhero setting, not to mention with a little work and the right paint scheme you could quite happily send him back to Weird World War or even further into Victorian Scifi.
Naturally you could do the same with any of the figures, but the effect of the Behemoth's pose is huge.