Sentinel 2: Earth Defense boasts a bevy of new TD weapons and enemies

Posted: June 26, 2009 in Tower Defense

A few months ago when Sentinel: Mars Defense made its debut on the iPhone/iPod Touch Platform, it was done with no fanfare, and became an unexpected hit with the gaming community. In fact, I would say it caught everyone by surprise delivering innovative concepts to the genre on the fixed-path side of things with a sci-fi theme. Origin8, the devs behind Sentinel, have now released Sentinel 2: Earth Defense which brings additional maps, new weapons and a new mode that will test your strategy skills. It’s always difficult to make a sequel because concepts and personal preferences run their course. But, Sentinel 2 is a solid complementary, and for those new to the genre, standalone title that continues the legacy.

Sentinel is the name of the dropship with powerful weapons which require time to charge and recharge after use. In the meantime, the objective for the player is to defend various compounds from alien attacks. The storyline in Sentinel 2 focuses on the aftermath of the failed mission on Mars, and now, the aliens are launching an attack on Earth. This is where the saying “All’s fair in love and war” applies, although there isn’t much alien love in this game. Sentinel has been revamped with new weapons to fight the attack waves, and the updated OpenFeint online system not only tracks scoring but provides a way to discuss and share strategies with other players.

As is typical with tower defense games, money is earned by destroying enemies which can then be used to buy and upgrade defenses. In Sentinel’s case, that money also earns interest which adds a layer of resource management to the game. You don’t want to blow your entire wad by indiscriminately placing defenses when you can be saving up and earning interest to the buy bigger and badder weapons. Think of it as your Sentinel Rewards Card.

Two elements that were introduced in the original Sentinel are also back: the repair drone and the barriers and electrified gates. These were innovative ideas back then, and they remain innovative even now. I’ll get into the repair drones shortly, but you’ll want to get those as early as possible. As for structures, there a whole new set of barriers to protect, and I always found these barriers and gates a refreshing element in the original Sentinel.

One of the impressive things for me with the original Sentinel is the visuals and the smooth animation. Sentinel 2 retains much of the visual presence with the drag and zoom functionality. Watching animations such as alien beings continuously bashing barriers or teleporting from one place to another just adds flavor to the genre. Because the setting is now Earth, the game has a significantly different look along with a new soundtrack. In addition, the towers physically change when upgraded, which certainly is worth pointing out since not all TD games do that.

Sentinel 2 has two modes of play: Campaign and Mission. In Campaign mode, 4 maps are included with two sub-modes: Assault and Endurance with 4 levels of difficulty: easy, medium, hard and psycho. Assault follows the specific number of wave attacks format, while Endurance is a survival mode with unlimited attack waves. Only when a map is successfully defended in Assault will it unlock in Endurance. I know many will talk about the number of maps, but I think this is subjective. A typical map will generally provide 35-40 minutes of play on normal speed (a fast forward button is included), and provided you succeed, Endurance mode with unlimited attacks will provide plenty of replay value. What would’ve been a good addition is the inclusion of non-fixed path maps to add a new flavor to the mix.

The new addition is Sentinel 2 is the Mission. It’s a new take on achievements much more elaborate and requiring quick thinking and even faster reflexes. Mission provides 8 different scenarios that lead into an achievements system. The catch of course is that you’re are extremely limited in resources, must meet scoring requirements or ensure that barriers are not damaged. This really adds a good layer of mental challenge to the game because in some cases, you won’t have any resources to start at all. For example, one of the missions involves surviving 1 wave with zero resources. Obviously, you’ll need to sell and buy quickly and know where to place and move defenses.

As in the first Sentinel, Earth faces a multitude of alien enemies which include mutants, arachnids, and winged parasites. New ones have been introduced that can teleport from one location to another as well as more elaborate enemies that require more firepower to destroy. A good tutorial is included that provides details and statistics for each of the units, and you’ll want to be familiar with all the nuances of the weaponry. The weapons from the original are all here—Laser, Bomb, Slow, Beam, Sniper and Ion. But Sentinel 2 boasts some new weapons and elements including a booster tower, an energy drone and a new set of dropship weapons. Each weapon has its own specific strengths (range, potency) and the booster tower is a new tool that when properly placed can enhance the strengths of other defenses. Visually, it creates a network linking those defenses, and it’s an interesting device to experiment with. When properly placed, they can incrementally increase the power and reach behind weapons so holding off on buying additional defenses may make more sense in the short term.

The new dropship weapons—Homing Missiles, Attack Drone, Time Warp, Orbital Laser—are a new set of defenses that when used properly can deal significant damage. Through auto or manual targeting, these weapons slowly charge up during the game so you’ll want to be careful how you use them. It adds yet another layer to your defenses, and visually, they look great in action on the screen. For example, with the Orbital Laser, imagine a powerful beam of light that shoots down from above cutting across the landscape vaporizing enemies in its path. I have to say that the Attack Drones are fun to watch as they zip around blowing enemies apart and is well executed in the Sentinel scheme. Speaking of drones, the repair drone in the original would repair damaged barriers as well as generating additional resources by mining. The new energy drone companion will use those resources to further charge up the new dropship orbital weapons.

The controls are drag and place and upgrading defenses is done by tapping on the specific unit. Icons representing the various defenses are located at the bottom of the screen. A weapons toggle is located in the bottom right corner which brings up options for the drones and the dropship weapons. The screen looks somewhat cluttered with all the controls, and on occasion, the only way I could upgrade units located at the bottom of the screen was to zoom in the weapons icons were in the way.

As with TD games, the gameplay is pretty frantic and requires in some cases, quick buying, selling, and buying again because of limited resources. Easy mode should be a breeze for anyone who has played TD games to an extent. Hard and Psycho are insanely difficult and will test your mettle. As you progress through the maps, they become more difficult with as enemies attack from multiple points and entrances. Something I found unnecessary occurs after successfully completing a map. A message appears stating that new map has been unlocked and is now playable. It then takes you to a screen showing the new map, but is inaccessible until you go back to the menu…an unnecessary extra step.

Having gone through all this, I will say that I’m disappointed that non-fixed path maps haven’t been included in Sentinel 2. It would definitely add to the strategic thinking required for the game, and broaden the audience appeal. Both versions of Sentinel are solid TD games, and since the original release, I’ve seen the influence it’s had on the genre.

The devs have mentioned expansion packs, but the current release as is offers a compelling and engaging TD experience. Sentinel 2 is polished, and while the sci-fi them may not appeal to everyone, the TD experience should. If you’re a fan of the original Sentinel, then Sentinel 2 is a must have because it introduces several new elements that make it that just as compelling.

Albie Meter: 4.5 Stars (recommended for TD enthusiasts especially those who enjoyed the original Sentinel; even if you didn’t enjoy the original, new elements in Sentinel 2 make it worth trying)

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