Surprised no one's guessed this. Well, more hints then.
#21 - A game Nintendo has released on many of their platforms over the years, but its best version is actually a PC port.
Hint 2 - This game originated 3 characters who are playable in Smash Bros.
#20 - Metallic beetle flies over a narrow path hitting buttons on the floor to slay otherwordly entities in a weird trippy dimension: The game
#19 - A game where robots fight other robots to save humanity from aliens.
#18 - The name of this game's final boss consists of only one letter.