cr0sh:
I take it you've seen the Uzebox, right?
Nop, but I was aware of Gameduino : http://excamera.com/sphinx/gameduino/ (amost the same thing)
cr0sh:
I should think with a Due you could way more than that!
I prefer to do something really small (407515mm), cheap (<25$ batteries included), and Do It Yourselfable (Nothing below 0805 for the smd). The arduino due ALONE costs about 50$ and is huge (even without stacking a shield)... what do you thing about that ? If I want more power, I'll go develop games on android 
DuaneB:
Are you still developing this console ?
I've been working on other projects these times (3D printer, 64*64 led matrix...) but I'm back. I started drawing schematics this morning (and learn how to use the software yesterday night hehe). The inactivity is although because I trusted a guy who said he was interested in drawing electronics... two months later, he has done nothing, so I'm back as a lone wolf, as ever 
DuaneB:
What was your experience with these, could you for example run something with a large number of separately animated sprites like a galaxians clone running with reasonable refresh ?
No, you can't. The screen's communication is based on SPI, so it's veeery slow (but convenient). On my snake game for exemple, I don't refresh the whole screen at each frame : I only rease few pixels of the tail and draw few new pixels on the head. Don't even think about scrolling, animated sprite (or just a few) or overlay text. Moreover sprites uses a lot of RAM. I think you should try a 3.2" screen (240*320px) on 8 or 16 bits parallel bus. But be carefull, they run @3.3V. You can although overclock you arduino to 20mhz instead of 16mhz I hope this helps 