Suicide Mission (Mass Effect 2)
Final Mission (Metal Slug 3)
Ganon's Tower (The Legend of Zelda: A Link to the Past)
The Maw (Halo)
Really need to shout out Metal Slug 3's final level. It starts with an autoscroller in your choice of jet or helicopter, then a rematch with Metal Slug 1's final boss only for it to be the martians from Metal Slug 2/X, then your character being kidnapped by said martians with the army you were fighting's leader having revealed to be also kidnapped, so now you're working with the enemy to go get your kidnapped character and their leader back by going into space to chase after their mothership, storming the mothership, fighting off zombie clones of the kidnapped character while you rescue the real one, escaping, then fighting the final boss who is chasing after you while you're plummeting back to earth. All in one level. It was meant to be the final game of the entire series and it showed.
Someday, I too will become Florida Man.