Tower defense games follow a pretty predictable formula; build turrets, fend off waves of encroaching enemies, rinse and repeat. Radical Poesis Games and Creations’ Immortal Defense doesn’t really deviate from this formula, but it still stands out from the crowd by virtue of its original presentation and strikingly imaginative science fiction story.

The plot focuses on subject K, a man torn from his wife, newborn daughter, and physical body to be inserted into the heavens in ghostly form so that he can protect his home planet, Dukis, from an invading alien fleet. The conceit here is that interstellar travel has been made possible by a series of intricate, linear pathways which ships must jump through as they travel. In bodiless form, subject K has the ability to effortlessly float around these paths and set up defenses to intercept these ships.

It’s a clever means by which to explain how it is that the forces we attack are forced to follow such limited channels, and why they are unable to fight back. But beyond this sly rationale lies a surprisingly engaging narrative about a man who desperately wants to return to his body. Freed from his mortal coil, we watch painfully as he outlives his relatives, and standby as he is tempted by the notion that he might actually be some form of god.

These ideas are decidedly cerebral; concepts that probably would have been more at home in an Isaac Asimov novel than a casual game. And yet they give Immortal Defense a mood all its own, making it a tower defense game you’re unlikely to soon forget.

And its original look and feel only enhances its uniqueness. The visuals are composed of retro-style vector graphics, or lines of projected color. The narrow paths that enemies follow are no more than a pixel or two wide, and enemy ships and our defensive units are composed of similarly simple-but still appealing-lines and blocks of color.

You might think such simple graphics would impose limitations on effects for things like weapon fire and explosions, but that’s not true at all. Move the effects level slider in the options menu all the way to 100 and the game’s colorful, wildly kaleidoscopic energy effects will actually overwhelm the action in some of the game’s busier scenes, turning parts of the screen pure white.

In fact, the effects can become so intense that it is sometimes difficult to figure out what’s going on or even where your pointer is, which is about my only complaint with the game’s appearance. I recommend keeping the effects slider below 50 to ensure you always have a clear picture of what’s happening.

Of course, strong storytelling and pretty graphics only go so far. A game needs to be fun to play if we are to remain engaged. Luckily, that’s no problem here.

The "towers" in Immortal Defense are referred to as "points" that are actually facets of subject K’s personality, such as fear, courage, and love. A fear point is essentially a basic turret, firing a stunning attack at enemy ships to slow them down. A courage point delivers a modest yield attack and can pass through an enemy to hit others behind it. Love points don’t attack at all, but instead bind with other points to power up their effects.

There are 11 points in all, many with highly original abilities, such as the circuit point, which does nothing on its own but when linked with others creates powerful energy fields that damage enemy ships as they pass through them, and the pride point, which begins weak but increases in power with each successful attack. They can each be upgraded six times, growing in power and abilities with each level.

Most of the strategy comes before each level begins. We’re shown the winding, twisting path-which often looks like a spirograph-before the level starts, as well as test ship moving along its lines. We then set up nearly all of our points before doing battle, placing each defensive unit with an aim to ensure its particular attack abilities will have an effect on a high traffic area of the path or a place where enemies are forced to slow down. We may earn a few additional points as the battle progresses, but most of the currency-dubbed "cache"-we earn while playing will be dumped into point upgrades.

That’s assuming you even have time to spend it. Most levels take no longer than a few minutes, and since our pointer also acts as a movable ship with a weapon of its own, it can be difficult to spare it from the battlefield long enough to click on a new point and assign it a location.

But the brevity is appreciated. It makes Immortal Defense the sort of game you can play for just a handful of minutes or several hours, should you let it sink its hooks into you (it has that just-one-more-level sort of lure that can keep players going all night).

The six linked campaigns will likely take most players seven or eight hours to work through, assuming they choose a somewhat challenging difficulty level, and plenty of additional fun can be had via the included level editor, which provides a simple and accessible toolset to allow players to create their own levels.

Immortal Defense‘s unique story and aesthetic probably won’t be for everyone, but those who cue to its surprisingly compelling and intricate mythology and original art design will find it well worth the investment.