Star Defense is a noteworthy addition to the crowded field of tower-defense games on the iPhone and iPod Touch. In addition to tight game design and lavish effects (both audio and visual), Star Defense introduces a substantial twist to the genre: a 3D space environment, in which you fight the insectoid S'rath on small planets that you can quickly twist, rotate, and zoom in and out on.
Waves of S'rath march toward your fragile colonist base on a set path through trenches on the game's seven different planets. You can choose between five different types of defense towers to stop the onslaught, following a calculus familiar to any fan of the genre: you have to place towers precisely to take advantage of each well-designed world's unique geography, while weighing the various tower types against each other (all with their own damage type, reload rate, and shot radius) and deciding when to buy new towers and upgrade or sell existing ones (each tower can be upgraded twice, and every level has a maximum number of towers).
You execute your battle plans in real-time against a set number of enemy waves (between 20 and 60, depending on the level, at Easy, Normal, or Hard difficulty), and this is where Star Defense's 3D-schtick sets it apart: while the core gameplay is relatively simple (unlike the complex upgrade paths and open-ended resource-management quandaries of other tower-defense games), Star Defense excels at immersing you in combat, forcing you to spin the battlefield back and forth to monitor progress and scout out terrain. The sights and sounds of combat even get more vivid when you zoom in making this a more visceral, rather than purely mathematical, tower-defense experience.
We'd like to see an online leaderboard to log scores and achievements (currently you can share challenges via Twitter, Facebook, and e-mail), and more planets would go a long way toward improving the game's replay value--but overall Star Defense is a fresh, fun, reasonably priced addition to the genre, and a must for tower-defense fans.