Puzzle Quest. It utterly wrecked my life last semester until I finished the campaign with two different character classes. Jesus, it’s an RPG with Bejewled attached; how can you NOT get addicted?! I personally love it on the DS, but if you have it on 360, PSP, or PC, don’t rebuy it. Otherwise, imagine getting to cast spells in your Bejewled map to make it go better, all while competing against an enemy, exploring a map, and building a small army of stat-enhancing mounts.
Magical Starsign. I don’t know anyone who’s played it and hasn’t liked it. Cute story (too cute?), but the gameplay’s pretty deep thanks to the lunar-based elemental damage system. It’s kids in space, fighting enemies and solving mysteries, but damn if it’s not fun as hell. And seriously, cute as a button.
New Super Mario Bros. I was just blown away by the sheer amount of fun and depth in this game. As much as I enjoy 64 and Galaxy, I’d been pining for a Super Mario World/Mario 3-esque game for years, and this fit the bill perfectly. Everyone on earth says it’s super easy, but I’m stuck on World 5 atm. I’d add more description to this, but really: it’s map-having 2D Mario. If you don’t “get” that, then please, buy an NES/SNES.
Phoenix Wright (any of 'em). I’ve never even touched one. But I’ve watched two separate people be slowly torn to shreds by the awesomeness of this series. I miss my friends, I really do. If you want the adventure gaming but would like some Indie Cred instead, grab Hotel Dusk. Solve court cases by sniffing out evidence, questioning witnesses, and dealing with drama. . . point and click adventuring at its finest. HD does the same, except you’re a detective and it’s all noiry and shiz.
Elite Beat Agents. Once again, a total life-wrecker that may also end with you breaking your DS in half or stabbing it with your stylus repeatedly. I, for one, had to hear a particular Good Charlotte song far more times than anyone should ever have to, so you might want to consider importing the Japanese version. It’s a rhythm-action game involving a lot of tapping, spinning, and dragging of the stylus, but the aesthetic is bizarre enough to make it work like new.