Sentinel 2: Earth Defense is the exciting follow-up to the original Sentinel: Mars Defense. There are surely too many tower defense games on the app store today, but both of these games surpass the competition by leaps and bounds. Sentinel 2: Earth Defense offers a remarkable combination of superior graphics, creative and functional menus, a quality soundtrack, and superior gameplay. If you are now thinking that a tower defense game can’t that good, keep reading and then just buy the game and decide for yourself. I had not even played a tower defense game before I got my iPod, but I now love a few select greats, and Sentinel 2: Earth Defense is the best of them.
Sentinel was not one of the first couple of waves of tower defense games to hit the app store, so many people overlooked the game as a copy-cat, but I can assure you that it is very original. When I first picked up Sentinel: Mars Defense (the original Origin8 Sentinel game), I had just taken off on a four hour flight. I thought I would try the game out for a few minutes, but I really didn’t expect much. Well, to sum it up, when the flight attendant came by and asked me to put away my iPod, I was shocked. I had been playing for about three hours straight, and I had fun the whole time. Part of the reason that I could play a tower defense game that long is because it actually requires strategy. I spend a good amount of time dying at the beginning and then tweaking my strategy and trying again. Sentinel 2: Earth Defense is even better, and I have to applaud Origin8. If they keep brining titles with this level of originality and polish, they will become the best of the best in the app store market.
Upgrade System: Sentinel 2: Earth Defense has a very good upgrade (or money) system. Tower defense games utilize a number of different methods for upgrading towers and abilities, but many systems are just too simple to sculpt that ultimate strategy. This is the exception to the rule. Sentinel 2: Earth Defense gives the player upgrades for each tower and upgrades for your ship (you are given four different attacks from your ship which help to supplement your towers). The towers use money for upgrades (which are earned with a combination of killing enemies and interest), and the ship uses energy for upgrades. If that doesn’t already sound like a great upgrade system, there are also up to three repair drones that have to functions 1) they repair the gates that hold off the attacking enemies and 2) when there are not any repairs needed or if you tell them to they will mine more money that will get added to your total on a periodic basis. You can also buy three drones that harvest energy or increase the frequency and longevity of attacks from your ship. If you don’t like this upgrade system, I will be very surprised.
UPDATE: A notable difference between Sentinel: Mars Defense and Sentinel 2: Earth Defense is that the tower upgrades are different for the last upgrade. This makes a big difference in terms of strategy. In Sentinel 2: Earth Defense, the first upgrade is the same price as the tower and brings it from 1 damage to 2 damage (depending on the type of tower, but the ratio stays pretty similar), the second upgrade costs the same as the original tower cost and brings the tower from 2 damage to 4 damage, and the final upgrade costs three times the original cost of the tower and brings the tower from 4 damage to 15 damage! That means upgrading requires a good strategy and placement.
Menus: The menus are polished, fit the theme, and work perfectly. The menus really couldn’t be better.
Difficulty Balance: I think Sentinel 2: Earth Defense does even a better job that the original at balancing the difficulties from easy to psycho (four in total: easy, medium, hard, and psycho). Of course, easy is very easy for a veteran, and psycho is a great challenge! I play on medium if I wanted a relaxed game or want to score high points or a achieve a goal (like keeping enemies from advancing farther than a point I pick), and I play on psycho when I want a touch challenging game what will test my strategy.
Polished Graphic and Backgrounds: While the backgrounds are 2D, they are done with such high quality, that they really do look 3D. Also, the animations of the towers and enemies are top notch. Origin8 did not need to go to these lengths for a tower defense game, but they did, and I am very glad! Additionally, the towers actually change appearance when you upgrade, which I think it a big bonus because you can easily identify where your upgraded towers are. The other nice thing is that the sound effects do not take away from the graphics or animations.
Variety of Strategies: Many TD (tower defense) games offer one main strategy to win. In other words, there is a ‘right way’ to play the game. Sentinel 2: Earth Defense leaves the strategy very open to the player. You can play the same level many different ways and still come out on top. Of course, you have to learn the pros and cons of every tower and ship weapon, but you can use them creatively as the player.
They also added one more tower that increases the damage of other towers, and I think that helps to keep the strategy even more open for the player.
Limited Types of Enemies: I would like to see more enemies or types of enemies in updates. This is not to say that the enemies are very limited (there is more variety than the first), but I get tired of seeing the same enemies after a while. This is more just a personal preference than anything else. Perhaps as you progress levels, the appearance of these enemies could change a little.
In case you can’t tell, I was absolutely blown away by the quality and polish of Sentinel 2: Earth Defense. I highly recommend this title, and I would go as far as to suggest you buy both Sentinel: Mars Defense and Sentinel 2: Earth Defense for a combined total of $3.99 (Sentinel: Mars Defense is currently on sale for $.99). You will not regret either purchase, and you can’t spend your money better on the app store.
Sentinel 2: Earth Defense was developed by Origin8 and is available for the iPhone and iPod Touch for $2.99. I played through version 1.1.0 on an iPod Touch 2G.