Developer Kenny Sun is best known for his unique puzzle games involving geometric shapes. Each of those games picks a shape and builds a puzzle experience around it that tends to differ entirely from the developer's previous games. There are some common points, of course. The games usually have a ton of levels, each one introduced with a card stating that it was made by Kenny Sun. They're also typically audiovisual treats, albeit abstract ones. A Hollow Doorway [Free] follows in the footsteps of games like Yankai's Triangle [$1.99] and Yankai's Peak [$1.99] in some ways, but it's different in that this is more of a game of reflexes than considered thought. It has this developer's usual flourishes, but in terms of mechanics, it's closer to something like Super Hexagon [$2.99] than the positional puzzles seen in the last couple of Sun games. You control a hollow doorway. Some may call this a rectangle, but I assure you that it is a hollow doorway. Sliding your finger left or right will spin the doorway, and that's about all you can do with it. Luckily, that's all you have to do with it. What you need to do is to position the doorway such that it lines up with the outer doorways closing in on it. You can be off by a little bit, but if you're too far in one direction or the other, the doors will crash into each other and you'll get a game over. Line things up right and you'll earn some hollow points and move a little bit closer to the end of the stage. A percentage counts upwar...