Graphics are not most important part of game. They are important. But you don't need only graphics to make everyone play your game. They can be just two colors and be awesome.

What I learned from this...  that I really love shrimps in little suits?

Joke aside, I would say I learned that you can get VERY creative with only black and white lines as your toolset.  In a way, much more than in color- they can be many many things depending on combination and context, so you don't need to make as many assets in the first place. You don't need to draw grass, just texture it a little, and wow, you suddenly have grass...
I also learned a lot about making puzzles! They evolved quite a bit as I was making the game. I'm also learning about having intelligent design, so you don't need lengthy explanations to understand what's going on...  but that's a work in progress. (for example, you can open up a menu in my game, but it's optional and I didn't mention it so I didn't see anyone actually try...)

This was a thoroughly enjoyable learning experience in the end ^^

I learned that i ***really*** need to learn how to do proper level design :P