Angeal vs Genesis vs Sephiroth. An amazing piece of art which is part of the great task of characterization made by Square-Enix on FFVII: Crisis Core.
Extra Credits: Super Mario Bros. A great sample of the work done by Extra Credits youtube channel, which's one of the best educational sources I know about game design and videogame culture in general. I love how this short video shows what game design is about.
Because Games Matter - A Better Vision. As my Bio reads, "I take games very seriously, and I love them". This video provides a little taste of "why".
Honorable Mentions:
Great level design and the artistic expression of mathematics. Just as it reads. Very cool Portal Level Design review and interesting stuff such as Doppler Effect in videogames.
No Gendered Mechanics - How Genre Stereotypes Limit Games and Players. Theme matters. (The song from the ending rocks, just for the record)
Storytelling. "Every part of a game helps to tell its story".
Understanding the Fantasy.Study the fantasy you're trying to deliver.