I've played metroid on the DS, and have to say I wasn't that impressed. The graphics are only marginally better than the N-Gage. The interface itself itself is, well - shit. A confusing array of controls and using the touch screen centre to navigate requires more hands than a mutant money. The only plus was the price, $125 - £80, but I'm sure we'll be treated to an extra 25% of that when it's released.
I was hoping an all in one device: mobile, mp3 player, media etc. to storm the market but, as the N-Gage prove, this is easier said than done.
Moan over, I do like the look of the PSP but the built-in-battery that means everyone doesn't have an iPod could also spell disaster for Sony