I'd suggest Final Fantasy III and IV, Pokemon Platinum, Heart Gold/Soul Silver, and Black/White plus their sequels.
I know this is mainly abt DS games but there are some great Gameboy games you could get for your DS.....The Zelda games such as Minish Cap and A link to the Past, Crash Bandicoot, Mario Kart GBA, Pokemon Sapphire/Ruby....
This. Though I haven't played Virtue's Last Reward.Buy 999, now.
Yes the game is incredibly terrifying at points and the descriptions of mangled corpses are horrific, but it's a game you don't want to miss. If you're still on edge, then buy the sequel Virtue's Last Reward. The atmosphere is less intense, but the game is bigger and just as awesome.
Or... get both.
I'd suggest the Trauma Center games