Skies of Arcadia. I got it on the Dreamcast (oohh yeah!) when I was 11 (in 2001), nearly got to the end, my friend accidentally deleted my save, then a few more tries later I still hadn't finished it when my dreamcast went bust. Even after getting a new one. Then it came out on gamecube and I tried again, but lost a bit of interest somehow. But then, in 2008, after telling my friends this they urged me to finish it, and watched every hour by coming to my house every night. I finally finished it that year and since then have done it again this year.
Its just the game that holds deep in my mind, and that I'll never stop wanting to play it again.
Valkyrie Chronicles was similar, although I've only done that through twice.