Implementing a hard drive for the low capacity of 12GB (by today's standards of top-shelf players).

Fitting a very small screen onto a round exterior. Square Peg, Round Hole. Ugh!

Super tiny text on an already small screen.

Color screen though color not effectivey used to make the screen more readable. The shots I've seen may as well have been monochrome.

Round bottom makes it probable that dock-like accessories will be non-existent.

I'm in a rush or I could go on.