TapBoom is a rare game in that the title pretty much explains the entire story. You have a square and you have a line. The line moves quickly toward the square and then past it. When the line is at all touching the square, tap the screen. If you're too early or too late, you lose. Otherwise, tapping while both are touching causes the square to rapidly explode into a series of blue squares in celebration. Tap. Boom. That's seriously the whole game. It's free for iPhone and iPad and requires iOS 8.0 or later.
The design of TapBoom stays as bare bones as possible. It's a black background with white text and shapes. The end. The only shred of color present in the app reveals itself if you're successful at tapping the screen with perfect timing - the "boom" part of TapBoom.
Don't even try to predict the app and build up skill using muscle memory. The first three levels are a natural progression from a slow-moving line to fast-moving. After that, the speed of the line and the placement of the square completely varies. Level six could have the line moving at lightning speed while seven brings it to a slow crawl, which is a huge throw-off.
When you tap at the wrong time, the game is over. There's no turning back, sorry. TapBoom keeps track of your score and your high score. If you tap anywhere on the "Game Over!" screen, your very last move fades in. This allows you to stare directly at your mistake indefinitely, which is what I always love to do during my spare time.
There's no real multiplayer mode in TapBoom either, at least outside of the Game Center integration with achievements and challenges for other friends. What's incredible is that out of all the players, the all-time high score according to Game Center is only 34. That's how difficult this game is.
The simplicity of TapBoom is fantastic for luring you in though. If you download it, chances are you might be addicted for a while. It's not so difficult that it's frustrating. Rather, the pace of the game is so fast that it's easy to get lost in the cycle of replaying it just to keep trying for a new high score.
The gameplay and design both remind me a bit of Circle, in which the object is to keep tapping so the circle never touches the line it surrounds. It saw moderate success in the App Store, so if you enjoyed that title you might benefit from giving TapBoom a try. The difference is TapBoom's rounds come in short bursts and aren't continuous.
Overall, the game has a significant amount of the right ingredients to be solid, addictive, but not overly frustrating or difficult. It has no in-app purchases either and only a small banner ad at the bottom that stays out of the way.
TapBoom is a completely free title available universally for iOS in the App Store.