I played "Retro Mode" on my original Game Boy Color and loved it! The game is very entertaining and offers a great varity of gameplay/scene.
Chapters 3 and 4 are good balanced challenge! (I had two game overs in Chapter 4 , but still made it to the end and bring back home my cheese)
Fabulous pixel art and music! GG!
Oh, and I immediately recognized you from your drawing style. It was like, "Hey, that's the guy who did the animation of the kid falling into his Game Boy."