1- Terraria because best sandbox ever
2- The Binding of Isaac because best roguelike ever
3- Cave Story because plot
4- Shovel Knight because level design
5- Sonic the Hedgehog Franchise because my childhood
But I also love:
Team Fortress 2 (favorite first-person shooter), Don't Starve (favorite pointing and survival), Mario fangames (interesting), Megaman Franchise (favorite sidescroll shooter), Pokémon Franchise (favorite RPG), Final Fantasy IV, V an VI (another great RPG), Assassin's Creed Franchise (interesting set of abilities and good plot), King of Fighters Franchise (favorite fighting game) etc.