I certainly can't deny that i really like Yoshi's Island!
I also took inspiration from palette limitations on some old 8-bit consoles (specifically how they could only show 4 colours in a palette at a time). With a few exceptions on background elements I used that as a creative limitation. So every individual bit of dot art is limited to four colours (usually white, black + 2 others).
The player sprite being 'unpolished' might be due to it being the first art i did for the game, and then not having the heart to change it later!
The reliance on encountering new gameplay/enemy objects it partly due to the simplicity of the gameplay. But later on old gimmicks get recombined in (hopefully!) interesting ways. The final area introduces relatively few gimmicks but i wanted to have a "Show me whatcha learned" feel happening with that.