A DSi? Ewww....
Anyway, personal opinions of the DSi aside, seeing as my bro and myself imported the Japanese version of PS0 and recently acquired the English version of it, I'd say it's a pretty good game. If you played Phantasy Star Online or Universe before, PS0 plays similarly to those (although it shares far more gameplay properties from PSO then PSU). I'd probably be playing Phantasy Star 0 more often if my DS's L button worked. (grumbles)
If you'd like game recommendations for the DS, I'd say the three Castlevania games are really good, the Kirby games are good, and Tetris DS is pretty good too. The Ace Attorney games are also pretty good, but you may not like them if you're not big on the adventure, or "visual novel," kind of games.