The portable gents at Modojo have put together their top 15 original Game Boy picks, excluding the obvious Tetris. From the article: "This time we chose to highlight 15 grayscale warriors that have stood the test of time, and emerged as classics, despite appearing only in shades of gray." The list includes such notable titles as Nintendo World Cup, Metroid II, Kid Icarus: Of Myths and Monsters, Castlevania Legends, Link's Awakening, R-Type, Final Fantasy Adventure, and Kirby's Dream Land.
I haven't played an original Game Boy title since I was a wee tyke. Maybe color is overrated.