I created a couple Levels with the Editor provided for Portal 2. My goal was to learn about how to lead the player through a level and how to teach new mechanics. You can find those levels on my page in the Steam Workshop.
My main challenge was using only a select few elements in different combinations to create interesting situations for the player.
I uploaded the levels to the Steam Workshop and got featured on the main page with one of them. I was really surprised that it got 350 views and 250 positive ratings there, since I created those levels more as a learning experience for myself.
My goal was to introduce the player to the button-cube mechanic as well as to the momentum while moving through portals.
The first section introduces the player to the button, since he will likely trigger it while entering the level. He has to move the cube onto the button to be able to proceed.
The second section shows the player how momentum works in portal. He sees the cube falling through the portals and has to apply that knowledge in the third section.
This Level introduces the player to a lot of new mechanics. Mostly “Aerial face plates” (that throw objects) and players on a set trajectory in the air, timed buttons and cube droppers. In the last section, the player has to solve a puzzle to combine the mechanics he learned.
This Level is the trickiest one. It uses all of the mechanics introduced to the player in the earlier stages. Some of the actions need to be performed while the player in in motion and during a short time window. This level got the best rating of my levels and was featured in the Steam Workshop for one day, since the audience were players who are already familiar with the basics of Portal 2.