Sentinel must be the seven hundredth tower defense game to be thrown onto the iPhone. The App Store is practically drowning in the things. People keep buying them so developers keep making them. This time around it is a space alien tower defense game.
I don’t think tower defense games need much of an introduction. If you are reading this site, chances are you have played one or two in your time. But just in case, I will humor you. Tower dense is a style of game where you are presented with a maze of some sort. You are tasked with defending the goal at the end of the maze through the use of towers. In most games there are many different types of towers for different kinds of enemies. The goal is to outlast the enemy through clever placement of towers and resource management.
“So what is so different about Sentinel that would make me want to buy it,†you may ask. Not much. Sentinel is very tried and true. You have four different towers you can place, one for all types of units, one for bulk ground units, one for air, and one that slows enemies down. You have five different enemies that charge your base. Normal ground, fast ground, heavy “bossâ€, air, and a type that is immune to slowing towers. Nothing we haven’t seen before.
One cool thing is that you have a wall about midway through the level. If a wave makes it past all your towers it will get stuck against the wall until they manage to break it down. This gives your towers more time to hammer away at them before they are out of range. Once the monsters have been destroyed you can buy a total of three droids to fly out and start repairing the wall. Given enough time they can have your wall back up to full health.
The best part of Sentinel is it is free! That’s something every gamer likes to here. For the moment at least you can pick of Sentinel for nothing. It is part of a trilogy so for a “full†game you have to drop some cash. But the free version comes with four levels, two modes, and four difficulty settings, as well as OpenFeint support.
If you are itching for a tower defense game then Sentinel is your game. It is a totally stable, totally fun, totally generic tower defense game.  It is quite fun but brings nothing new to the genre. Much like first person shooters on console now a day, if it isn’t doing something new then why would I spend my time playing it?