Gotta Protectors is a great “2D Musou” game, Bloody Vampire is a fun Metroidvania style game with bump combat, Legend of Legacy is my favorite SaGa game (it’s not a SaGa game) and The Starship Damrey is a short first-person horror adventure game.
That’s all I could think of at the moment. All except Legend of Legacy are download-only games, so they are lost now.
Sadly most of the really short games I can think of were download-only games, so they are lost now. But if you don’t care, I’d definitely recommend the already mentioned Attack of the Friday Monsters. I really liked Ikachan which is very short (under an hour), it was made by the same person who made Cave Story, I think. I could be wrong about that. Bloody Vampire also was a nice and simple Metroidvania style game.
As for actual retail games, I guess the Kirby platformer games would fit that description. The 3DS ones, especially Triple Deluxe, are some of the better ones in the series. The Mario & Donkey Kong games are also rather short, but really nice puzzle games.
Just watched a trailer. This looks very, very weird. lol