Sentinel - Tower defense (TD) iPhone games have proven to be a genre that can be done extremely well on the iPhone. The cream of the crop in this genre currently includes titles such as Fieldrunners, 7 Cities, The Creeps, and they all have their own quirks that make them unique. That hasn’t deterred Origin8 from delivering its spin on the space with the release of their new title.

There are two primary modes in Sentinel named Assault and Endurance (has to be unlocked) to get through. Assault (think campaign mode) provides up to four difficulty settings that be chosen over the course of the game’s two maps.
Your job in Sentinel is to place weapons and defenses on a map to destroy waves of alien monsters that have different strengths and weaknesses. Upon seeing the enemy types, it’s your job to layout a variety of weapons and defenses to counter what the enemy is bringing. For example, flying alien critters are best handled by “Laser” or “Beam” tower defenses while land monsters are best handled by “Bomb” and “Slow” tower defenses. Killing enemies gives you cash to upgrade towers or buy new ones altogether. With each passing wave, you can earn points that accumulate over time. When your game is over, you can upload your score to online leaderboards to see how you compare with folks all over the country.
Sentinel adds a few sprinkles to the TD formula that is worth nothing. Most TD games lay out a map without obstructions allowing enemies to freely navigate through the path to attack your base. Sentinel adds in obstructions and barriers that enemies have to destroy throughout the map before they can continue unimpeded to your base. This adds an additional layer of strategy as you’ll have to make choices about concentrating your towers around those barriers or spread towers all over the map. Cool repair droids (which cost money) can be bought to repair barriers that the enemies are chipping away at as well. Last point in this vein, Origin8 has integrated functionality to speed up Sentinel by pressing an onscreen toggle button. Good stuff all around here.