The tower defense genre is very popular. The concept is simple: place defensive structures strategically on a map, use your gold wisely, and kill all of the enemies before they can reach your base, castle, home, or whatever else you are trying to protect. TapDefense for iPhone takes this formula and marries it with a throwback graphical style from the 1990s, numerous maps and objectives, and a slew of different types of enemies to create an engaging but often frustrating entry in the genre.
TapDefense is very similar to other tower defense games. You start with a certain number of coins that you can spend on defensive structures. Place those structures wisely and they will automatically attack enemies as they approach whatever you are defending. If you kill all of the enemies before they reach the goal, you win. If you don't, you lose. The concept is simple, but the execution is theoretically hard. As with any game in this genre, TapDefense starts out very simple. It gets harder, but never quite reaches the level of painfully hard. There is a very distinct lack of originality in the towers and enemies you face, however. For those eager for a casual, easy-to-pick-up tower defense game, TapDefense is a good place to start. For serious TD gamers, it probably doesn't offer the difficulty or depth you're looking for.
Having not been updated for the iPhone 5 and its larger screen (and upgraded operating system), the game is a little buggy. While we had no issues with save points as has been reported for some devices, the lack of iPhone 5 support made it hard to engage with all of the game's features. The layout, execution, and style of the game is cool enough to warrant a download, especially since the game is free, but in terms of its standing against other tower defense games, there are those that offer more maps, more variety, and better overall support.