Let me get this out first: This game's artwork is fantastic, some of the best art I have seen in any game (not techically, but artistically). It has 60 hand drawn screens, and they are all beautiful. Take a look at the picture; that's the kind of art that fills this game and gives it life. The artwork alone almost justifies the $15 price tag.
Then there's the gameplay. This game is casual gameplay personified. Most of the game is spent scouring the landscapes for puzzle pieces, and pieces of puzzles (if that makes sense). For example, say you need nine lightbulbs to solve a puzzle. First, you need to go find nine lightbulbs, and the item hunting takes the form of a hidden object game. Usually I don't like hidden object games all that much, but I'm willing to make an exception for this game, purely because of the art. Then, once you have all nine lightbulbs, you go back to where you were assigned to find nine lightbulbs, and you solve a little puzzle, Proffesor Layton style. The puzzles themselves aren't very difficult (except for one near the end that isn't explained very well), so most people will have no problem whatsoever making it through the game.
The sound for the most part is okay. The music is unobtrusive, and goes perfectly with this strange little world you're trying to put back together. The sound effects are fitting, but I think it would've been nice to have more than one fly collection noise, it gets annoying after a while.
On the replayability side of things, there's not much. You play through the game in a little over two hours, a very short time considering the price, and then you're pretty much done. You can replay all the puzzles, but that's about it. There's really nothing left once you finish the game once, unless you want to look at all the artwork again, which i would definetely do.
All told, The Tiny Bang Story is mostly eye candy, but with just the right amount of gameplay to complement the artwork perfectly. Exploring this world is a joy, even if you just do it for the art. Sure the price tag is a little (okay, very) steep at $15 for two hours of gameplay, but it's worth it to support this budding game developer. Try the demo on Steam. If you're wowed by the art, buy it, even if it's just so these people keep making games. You'll be glad you did.