Wow, it makes me feel so good to see the GP32 and the GP2X starting to become well-known on these boards.
The MKII is very similar to the MKI. Notable differences are a much improved stick and a more vibrant/brighter screen (The MKII doesn't have that scanline look like the MKI). Some people commented on worse viewing angles, but it was probably taken out of context and was referring to extreme angles (Basically angles that others would use to watch you play).
BTW, in case nobody here goes to GP32x, SquidgeSNES was updated yesterday with Squidge's new MMU hack. People have said that it's full speed with sound at ~270mhz and that it's full speed with sound with a lot of games without overclocking.