World of Goo is a physics-based puzzle/construction game. Here I have created a list of my top 10 small Steam games, they come is small packages (mostly under 200mb), have very little playtime (under ~7 hrs) and are hell lot of fun to play.
Games from big studios, with ultra-high graphics and games, are fun, no doubt about it, but small, simple and short games can be as much fun as those memory hogging games.