Fighting off swarms of alien hordes isn’t quite as exciting as one might expect.

I’m not going to lie: things look bleak right now. All that’s left of humanity is trapped in this tiny little space station, and our enemies are closing in on us from all sides. What’s that? You just arrived on the station and need some money? How about you take over here and start blasting aliens in exchange for some cold, hard, cash. Here, take this copy of Blast Radius on the iPhone and start getting ready. No, really, knock yourself out. Don’t mind me, I’ll just on the other end of the hangar preparing my little escape shuttle.

At its core, Blast Radius is a tap-defense game with a one slight difference: instead of tapping the invading aliens, you have to place bombs in front of them. The blast radius (aha!) from these explosives spreads out depending on how long players hold their fingers on the screen. The longer one holds their finger on the screen, the bigger the radius, which can be useful when multiple energies are approaching. The space station has a force field that appears in quadrants around it; each section can sustain one hit from an alien, but its game over if that area is hit again before repairs are made.

However, there’s an energy bar at the top of the screen that will drain when the blast is charged. As a result, players have to let the bar recharge if they unleash a big blast, which can mean a quick death if there are more aliens on the screen. It takes a little getting used to, but once players figure out how they need to place the explosives and how long they should charge them for, there’s a fast-paced strategy element that can prove to be pretty challenging.

The more aliens one kills, the more credits are earned, which means that players can buy upgrades like faster energy recharges, station repairs, interest on credits, and more powerful weapons. Players can also buy currency with real money, courtesy of an in-game store. In order for humanity to survive in the face of its enemies, upgrades need to be picked up so that players can keep up with the on-screen enemies.

Visually, the game is sort of mixed. The background design and central space station look great, but the actual enemy units sport very little detail and look rather fuzzy; seriously, some of the enemy ships are little more than glowing orbs that blink as they float around the screen. Not only that, but it’s sometimes difficult to spot the aliens when the brightness is turned down on the iOS device. The music and sound effects, in turn, are fine, but a little generic. The soundtrack features a rather minimalist score that works, but isn’t really all that arresting.

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Overall, Blast Radius is a decent defense title that is saved from mediocrity thanks to a rather unique gameplay mechanic. It’s interesting, but not exactly anything to write home about. Still, the challenge is moderately enjoyable, so checking out the free version of the game is probably the safest route in this case.