To answer your question about the GAME MP4 player (the OEM ones from china) : i have two of them lying at home, and i must say i'm impressed with them !!
First of all, the screen quality is wonderful ! Much better than the nano clone mp4 players, and with 2.5" QVGA (320 * 240 i think although the manual says 960 * 480 ??) resolution and perfect contrast. Ideal for viewing a movie !
Next, it hasn't crashed since i used it the first time (2 weeks ago) which is also a good point.
You have the basic functionalities like probably mentioned in the ebay ad : mp3 playing, movie playing (mine does .asf format). Also it has a tv-out (all cables included) and you can even record from a movie source through a AV-in connector (using the same cable). Ofcourse you can also record music through the line-in connector.
Next, it has a digital camera built-in : don't expect super quality (think its a 0,3 mpixel) but it still is neat to use it : there are some filters built-in like negative, sepia colors. Also you have a 4x digital zoom, but of-course no flash, so shooting at dark places is not possible.
Next, it has a built-in speaker, that doesn't go that loud, but enough to play games on it ... see below.
And last but not least, you can play all nintendo 8bit games (.nes) easily available on the net. Like donkey-kong, mario bros ... the classics from the 80's
Oh yes, i almost forgot : you can get them with internal memory of 512mb, 1GB or 2GB (maybe also the 4gb, i'm not sure) but you can also expand memory through the built-in sd memory card slot.
Any more questions, don't hesitate to ask !