You know what's one Neo Geo game that doesn't get much love?
Puzzled (aka "Joy Joy Kid")
People just pass it off as a boring Tetris clone without actually playing it. Weighing in at just 22 Mb, it's the most graphically primitive of the entire Neo Geo library. But it's the gameplay that matters most, and Puzzled excels in that regard. You don't simply clear lines, but instead must solve each puzzle to release the balloon at the bottom of the stage. As the game progresses the pieces begin to drop faster and faster. The game enjoys putting you at the edge of your seat, particularly when the "serious business" music starts playing. But all remains fair, and when you survive with your split-second decisions, it's an incredible sense of accomplishment.
To get the true ending, you also have to beat it twice Ghosts 'n' Goblins style. I've never done it.