Portability (size / weight)
Great display and some great games got the PSP off to a great start. Late to the game internet purchases and cheaper games could give it a shot. Sony blew its chance with its little techno wonder when Sony forgot basics like who wants a 250 dollar micro console and another 50$ games. Long load times (blame UMD), expensive memory stick, lame internet, weird accessory software to watch movies and music, heavy, and fragile. The PSP is the also ran of the portable wars.
The new Sony store shows promise with a huge PSOne library of emulated software. Cheap games and inexpensive memory now that the UMD has been ditched could give the PSPgo a new life. Most of the buyers have moved on to ipod touch and DSi.