No other genre has been so representative of iPhone and iPod touch gaming than tower defence. Only match-three puzzlers are more prolific.
It's easy to understand how tower defence arose from nowhere to define a new generation of hardcore portable gaming. By combining the critical thinking of a strategy game with incremental level design to ensure portability, tower defence has just enough depth to keep you hooked, but can still be played in a few spare minutes.
From the earliest days of the App Store, tower defence games have been at the forefront, from Fieldrunners to Star Defense. Yet there are plenty of fantastic tower defence titles in between (and, it goes without saying, plenty of bad ones). Here are our top tower defence picks:
Developer: Rough Cookie
It's not the stellar 3D graphics that make Star Defense a triumph, but rather the finely balanced gameplay that earns recognition as one of the best tower defence games on the App Store. There's simply no game in the genre that possesses such astute design, variety, and polish.
The concept is a fun one, too: beating back waves of S'rath alien invaders by plunking down towers on remote intergalactic outposts.
A small, but diverse set of armaments encourages strategic deployment and three levels of upgrades demand careful financial management. Beefing up your towers is critical to defeating the array of S'rath species that stream through each level's trench.
Leaderboards, awards, and push notifications keep the game on the cutting edge, providing a decent amount of replay value. New levels for purchase within the game are promised for the future, so you can be sure Star Defense will be defending its spot for some time to come.
Sentinel 2: Earth Defense
The threat of an alien invasion prompts a tower defence in Sentinel 2, the highly polished follow up that retains the path-based gameplay of the original. It's much improved here with an array of towers, upgrades, and special attacks that make it a solid addition to the genre's enormous iPhone library.
A four-mission campaign only kicks things off. The real fun begins with the tough objective-based missions and the endless Endurance mode. The latter is particularly challenging, if only for the fact that it tallies your best performances with others online.
Some minor issues prevent it from being ideal - more clearly identifiable paths, greater variety in enemies - but it's undoubtedly one of the best examples of the genre on the App Store.
Developer: Limbic Software
Publisher: Limbic Software
Tower Madness emerges from the humongous flock of tower defence games on the App Store thanks to a hilarious premise, impressive 3D graphics, and solid gameplay. There's no way you can fall asleep protecting the sheep in this free-roaming game.
Shepherding the aliens gunning for your sheep is the first objective, as Tower Madness requires building winding paths lined with towers. Varying these towers ensures you can beat a range of extraterrestrial enemies, from flying ones to lumbering bosses.
It's such a fun and funny take on tower defence that it's hard not to enjoy, even if it essentially sticks to convention.
Crystal Defenders: Vanguard Storm
Developer: Square Enix
Publisher: Square Enix
Unlike a traditional tower defence game, Crystal Defenders: Vanguard Storm has you situating a small squad of forces on a grid to combat enemies in quick wave-based battles. It carries the flavour of a tower defence game nonetheless, delivering inventive gameplay in lieu of tradition.
By blending the wave-based combat of tower defence with the character development of a tactical role-playing game, it accomplishes a new style of gameplay. Instead of spending money on upgrades, you aim to earn experience for your characters by thrusting them into battle.
Borrowing character classes and enemies from the Final Fantasy series doesn't hurt, either. Vanguard Storm heralds a delightful, fresh spin on tower defence as challenging as it is unique.
Developer: Subatomic Studios
Publisher: Subatomic Studios
No other game is as emblematic of tower defence, particularly on iPhone, than Fieldrunners. Among the first wave of games to arrive on the App Store last year, this colourful military adventure is a quintessential representation of the genre.
Presenting open levels within which you build towers to direct and destroy waves of enemies, the game opts for a highly polished take on the formula instead of risking crazy ideas. Land bound and aerial enemies are taken out with corresponding towers on five maps, two of which have recently been added in an update.
Cartoon-like graphics lend the game a lot of charm, which in part accounts for its unshakable following on iPhone and most recently PSP. Without question, this is your bread and butter tower defence that will satisfy any need for classic tactical gameplay.
Zombie Attack! Second Wave
Zombie Attack! Second Wave starts off on the right foot, putting the spotlight on waves of undead to be shot, sliced, and scorched by turrets placed with your fingertips. Not content to rely on the appeal of zombies alone, this inventive tower defence title introduces creative units and action elements as well.
Rotating axe blades on the choppa turret and the fake mannequin decoy encourage tactics not found in any other tower defence game. Combined with the ability to hack apart enemies with a machete, Zombie Attack! earns recognition for its fresh approach.
The only drawback is the slow-to-build levels that amble at a pace that would make a zombie seem like a cheetah. Get through these tedious opening moments, however, and you find a quirky take on free-roaming tower defence.
Developer: Super Squawk Software
Publisher: Super Squawk Software
Consider the nightmares of your childhood a reality in The Creeps, an absurd take on tower defence that has you beating back monsters that emerge from the darkest corners of your bedroom closet (and no, we're not talking about that one-night stand from last summer).
An array of knick-knacks and household items are all that's available for mounting a defence - glue bottles, flashlights, even toy guns serve as your weapons. Of course, the creeps that crawl forth from the closet are equally as bizarre.
The hand-drawn graphics lend a charm that's irresistible and a commitment to add more content via updates and in-app purchases puts The Creeps among our favourite tower defence titles.
Bloons Tower Defense
Developer: Digital Goldfish
Publisher: Digital Goldfish
The dart-throwing monkeys of Bloons Tower Defense may not be the 800lb gorilla of the genre, but they know how to throw their weight around. Expanded from its original web browser release, this blown up iPhone and iPod touch version is as challenging as it is fun.
Speedy waves of balloons give Bloons Tower Defense a higher tempo than many of the others on the App Store. To help you strategise against fast-moving enemies, you're given ample time to set down monkeys between waves.
What has us particularly impressed is that the content has been more than doubled since its web release. Joining the original six are nine new maps, which are sure to last quite some time when you add in leaderboards and achievement support via OpenFeint.
Developer: Brisk Mobile
Coming to iPhone and iPod touch by way of PC, Vector TD has been redrawn with the smaller touchscreen in mind. While there are some tricks to dealing with the condensed interface, the core gameplay remains as tight and tense as ever.
Sharing the same features and modes as the recently released PSP Minis version, here you're plunking down geometric towers to destroy shapely enemies that stream in from one end of the level in an attempt to make it to the other. Straightforward units make it easy to understand, though there's good variety with more than a dozen available towers.
More optimisation could make Vector TD work better, but even in its current form it's one of the best and purest examples of the genre around.
Plants vs Zombies
Developer: PopCap Games
Publisher: PopCap Games
It's hard to argue with the quirky tactical gameplay of Plants vs Zombies. No other iPhone and iPod touch game combines humour and depth of play at such a high level of quality, all without sacrificing the accessibility that made the original PC such a sleeper hit.
The 50-level Adventure mode packs hours of gameplay, with nearly each level introducing a new plant to use or zombie to beat up. Variety is definitely the game's strength, as it offers up more than any other in this list.
It's a phenomenal value for the price, too. Of course, we can't help but want the bonus modes included with the original game, but with such a low, low price we're willing to fork some extra money to in-app purchases in the future for them.