IMO, Tenshodo has a real winner with their new Z scale D51 Japanese Mikado. 16-wheel pickup, a smooth drive, great detail, fine flanges (.020, versus Marklin's .030, except for the pilot wheels, which are .025, likely for more reliable tracking), and the best valve gear I've seen in Z. Plus, the motor is in the tender, and reports indicate that it pulls quite well in spite of the fact that it has no traction tires.
I think the bashing potential for it is enormous. With a new shell it becomes a small, early American Mikado, or any variation of X-8-X. Lose the leading and trailing trucks, and you've got the start of a USRA 0-8-0. Lop off a set of drivers for an X-6-X. And it looks like the mechanism would be relatively easy to work into an articulated.
They've been selling like hotcakes at Hobby Search, selling out twice already before being restocked. I think it would be worth it for Tenshodo to look at the American market.

Robert Ray has good technical review of it here:
http://www.trainboard.com/grapevine/showthread.php?t=117124&page=3