I've still got things to unlock on Yu-Gi-Oh World Championship 2008 (DS) but as far as game completion is I've cracked Duel World. Just some tag duelists to unlock and also some duel disks and costumes to get.
I've taken a break from YGO Stardust Accelerator 2009, mostly because I'm not quite getting the hang of speed duels. Plus you have to face the best cards in the game right off when you have almost nothing to work with.
*Sigh*