What is great about Gamestar, is that it is well balanced between playing, learning and creating. The site ACTUALLY encourages its users to play the video games through their tutorials called "Quest." The Quest is a little story that has the look and feel of a Japanese Manga, but as you play the game, you begin to learn the basics of video game design and you unlock characters and items to include in your games.
In FACT, you can't even publish your game until you complete all five episodes. So, as a teacher, I feel that this is a great (and free) tool to use with my students. Some of the games may be a little simple and cheesy, and the kids may be a bit frustrated that they can't import/create their own characters, items, music or backgrounds, BUT it is an excellent way for your students to create something utilizing 21st century skills, heavily bound by STEM standards, read comics while they learn and share their work on the internet for the world to play.
And coming from a gamer's perspective, for someone who grew up with a Nintendo Enterntainment System in their home as a kid and has since gone through the several generations of video game consoles, I think is a great way to hook the students into their own interests. If you have a student that is interested on some day creating their own games, check this one out to just get used to the whole theory and practice behind game design, but if you really want to get crazy with video game programming, then I would recommend Scratch (which is a bit more complicated)