“Trenched” is a game in which disabled World War I vets defend the world from hostile, tentacled TV-robots by firing upon them from “mobile trenches,” which are sort of like walking tanks. Game developer Double Fine has had stranger ideas.

According to a 2010 gamasutra.com article, while at work on the developer’s last retail title, 2008’s “Brutal Legend,” employees were told to take time off and create foundations for new projects. “Costume Quest,” “Stacking” and “Once Upon a Monster” were built around narrative ideas, but “Trenched” is a downloadable game that spawned around the complaint that the passivity of the player that is forced in the tower defense genre is boring. So, why not build a mech-shooter around it?

Whether it’s “Defense Grid” or “Plants vs. Zombies,” the core mechanics of the Tower defense game remain the same. Players build turrets and other defenses in order to prevent waves of enemies from attacking their base. Each enemy drops more money, which is used to buy and upgrade gear. “Trenched” follows this formula, infusing a shooter into the mix. Properly outfitting your trench is as important as turret placement.

The result is a hectic action game in which you constantly juggle your line of fire and positioning, along with that of your emplacements, which are stationary defensive units that aid you in battle. Early missions are possible to beat without firing a single bullet, but you will eventually need to depend on your mech in order to beat the increasingly difficult tentacled TV-robots (called Monovisions). Some fly, some run toward you and some infuriate by spamming fire on turrets.

Outfitting your mech is crucial to each mission. After choosing a stage, you are given suggestions on what to bring into the battlefield. If the text says, “long range weapons” and you bring a shotgun, you won’t get far. You can also alter your mech’s body, allowing for a set amount of weapons and emplacements. Legs, for example, come paired with special abilities such as sprinting or quick reload. Each mech either comes with more firepower or more emplacements, but you can’t have a large amount of both.

With such an emphasis on direct combat, it’s a shame the mobile trenches don’t control better. The sluggishness of the mechs may fit the game’s post-WWI milieu, but it makes traversing the battlefield difficult. Those nostalgic for the speed and versatility of “MechAssault” will be disappointed to find these mechs are more on par with those found in the slower-paced “Chromehounds.” Stumbling upon geometry and getting a grip on the cumbersome sprinting ability adds an unnecessary challenge.

For a tower defense game, the turrets don’t feel essential to success beyond a few occasions. Emplacements come in three varieties: support, heavy and light. Support emplacements slow down enemies, repair your mech and help you collect loot. Heavy emplacements are useful for sniping distant enemies or bombing a horde of enemies. Since these two are limited to only mech classes with few weapons, relying on the machine guns and shotgun turrets of the light emplacement class is more convenient.

Between each mission you return to the S.S. McKinley, a large battleship where you customize your mech and move around with your avatar, which you can also upgrade with new costumes. On the ship, you can also recruit players to help you on a mission. With four players, some of the game’s larger maps become much more manageable. However, the difficulty scales and loot is more scarce. You’ll also have a difficult time finding a player who isn’t hoarding for themselves.

In fact, it’s a bad idea to play with strangers at all. Communication is key to winning or even starting a match. Since any player can select a mission — which starts a minute-long countdown — and anyone can cancel, obnoxious players on a quest to annoy others have the ability to waste everyone’s time. It’s one of many details that Double Fine overlooked in the game’s presentation and end-user experience. Selling and buying trench parts is another area the game could stand to improve. The biggest fault though is a purely technical one: Every match, of the 10 or so tested, suffered from severe lag.

Even in “Psychonauts,” Double Fine’s first and arguably best game, style ruled over substance. It’s encouraging to see the developer branch out into a creative strategy-action hybrid where story takes a backseat. If anything, the story often gets in the way of the action, forcing the player to listen to dialogue between waves of enemies. The game looks good, running on the “Brutal Legend” engine, but the art direction is surprisingly drab for a Double Fine game.

Whether you want to blind-fire on a sea of enemies or strategize your way to victory alongside three friends, “Trenched” has something to offer. It has its shortcomings and technical blemishes, but it wouldn’t be a Double Fine game without them.