My work modding Skyrim involved creating whole levels that were (hopefully) at a similar level of quality to that of Bethesda's own designers. I would pore over the Creation Kit for hours, retreading their dungeon design steps and rereading the official documentation to take note of all the features (and quirks) the engine had to offer.
The end results are two full levels, released a couple years apart. My most recent work, Volundr, has a 95% positive feedback rate on Steam and over 100,000 unique downloads between that platform and Skyrim Nexus. The feedback and encouragement I got from players exploring my levels spurred me to go full-speed toward my Digital Media degree.
Looking back, one of the most important lessons of my modding career was being able to conform to a vision. None of the assets in these levels are my own, but I learned to design with the overall game context in mind and think about how the artists intended their work to be used.