#2: Sonic & Knuckles
Many folks see Sonic the Hedgehog 3 and Sonic & Knuckles as one whole piece, and I see where they're coming from. For some reason, Sega split the game in two halves and bookended them in 1994. Seprated, they're both incredible games (and to be honest, S&K would be #2 regardless), but together they form an experience unlike any other. It's like if Empire Strikes Back and Return of the Jedi were combined. But I'd like to focus on S&K, which to me represents the very best in 2D Gaming. Incredible sprite graphics, unforgettable music, a simple yet engrossing story told through the gameplay, and some of the best pacing in gaming history (I can't tell you how much I adore playing from Lava Reef Zone to the end. It's so damn perfect.). Everything just flows so perfectly that I can't help but gush about it all. So I'll stop while I'm ahead and smile to myself as all the memories come flooding back. Truly a masterpiece!