Öoo

Öoo is maybe one of, if not the, smartest and most well-designed puzzle games I've ever played. Your little caterpillar (hence Öoo, get it?) finds itself trapped inside a bird, and has initially one and soon two body segments that act as bombs, that can be detonated to propel you upward, laterally, or to destroy barriers. And that's it. At least, at first blush. You'll use those basic skills in ways you can't possibly imagine later on, but the game never tells you what to do, opting instead to carefully design the levels and puzzles in escalating fashion, trusting the player to experiment and figure it out. When you drop into a new area, there are often two paths before you - one seemingly impossible, and another much longer one. There's no prize or weapon or doodad at the end of those longer routes - only a fast travel door to send you back to that initial fork. But what you do gain from that route is the knowledge of how to immediately bypass that previously impossible route. And that's kinda great!