I recently got 4 Japanese PC98 Sierra games: PQ2, QfG1, KQ5 & SQ4.
Out of these, PQ2 proved to be the coolest.
Here's what I learned so far:
The SCI0 games (QfG1 & PQ2) both have 2 display modes: 640x400x8 colors & 640x400x16 colors. The 8-colors mode is a dithered version of the 16-colors mode that use the high resolution for dithering (like the EGA640.DRV driver does for 256-color games). In the 16 colors mode the high resolution is used just for the Japanese text. The resources use 16 colors in 320x200 resolution.
(My version of) PQ2 came with a driver only for the 8-colors. I used the 16-colors driver from QfG1 with PQ2 and it works.
Here are some pictures:

16 Colors

8 Colors (Dithered)
Now for the really fun part:
PQ2 has slightly different views than the english version: They've drawn the faces in Anime style (like the japanese Zak Mackracken).
Here is an example:

English version

Japanese version
Cool, eh?

m_kiewitz from the ScummVM forums even uploaded a short video from this game to youtube:
http://www.youtube.com/watch?v=AHJbeTlARA4