Tower defence games can be pretty boring. Beyond the cutesy charm of something like Plants vs. Zombies, you're always doing the same thing: staving off waves of increasingly difficult enemies using a "rock-paper-scissors" mechanic of throwing down obstacles that your A.I. opponent is weak against. But even though Trenched is, at its core, just another tower defence game, the way it throws you into the action makes the experience feel new...or at least different enough that you're more worried about surviving, and less about "how many more waves do I have left?"
In Trenched, you still battle against those set waves of enemies, and as you'd expect, those enemies are weak against very specific weapons. But instead of just putting down towers (Emplacements, in Trenched's parlance) and passively letting them have all the fun, you get to take a more active role in the protection process.
The Emplacements you throw down supplement the loadout of your customizable, mech-like contraption. While you do face some obstacles that require specific solutions (like airborne enemies who should be taken out with flak canons, or armoured enemies who are only weak against mortars) the open way you're able to approach those battles is what makes Trenched feel unique.
The mech you choose has limitations, so you have to be strategic with what you bring on the battlefield; whether you want your own weaponry to focus on ground forces while your Emplacements take care of some other enemy is up to you. As you progress through the game, you earn new gear and abilities both by completing certain accomplishments (like killing X number of enemies with a machine gun) and by finding them on the battlefield. And that gear has the same colour-coded system you'd find in a dungeon crawler -- green gear is nice, but normal; purple gear is rare and powerful. So, both finding that special gear and filling up the accomplishment meters that track what types of weapons you've used keeps the game entertaining long after you've finished the campaign.
Trenched's multiplayer features help bolster what's already an addictive experience. There are no competitive modes, so when you play with friends, you're all trying for the same goal as the single-player campaign: protect your base and kill lots of enemies. But the game is more fun when you don't have to worry about taking care of everything yourself (though you'll face exponentially more enemies when you bring another person onto the battlefield). But there's just as much strategy in deciding who'll bring what weapons to the match in a group as there is in trying to customize your loadout in single-player.
Your mech can't jump (or fly, sadly), but the only time I ever noticed that beyond beginning was when my character got stuck on a ledge and was unable to escape out for the duration of a match. And it can be difficult to keep track of enemies, especially when playing on your own. Though they generally show up with arrows pointing where they're coming from when you're not looking directly at them, sometimes those indicators are strangely absent.
That can sometimes leave you wondering where an attack is coming from, or why a round hasn't ended, even though you don't immediately see anything left to kill. And though the game's clearly based on the tower defence model, you never get a chance to see a strategic overview of the playing field once you're in your mech...and sometimes I really just wanted to fly up and look at the battlefield from above just to get my bearings and plan my strategies.
But those are small problems in what is otherwise a wonderful, simple game. The coloured loot calls out to the loot hound in me, and the customization option available for both my mech and his pilot make me want to play a few more matches just to earn the money to trick them out differently. Trenched's campaign isn't terribly long, but like Double Fine's other recent downloadable games, it's completely enjoyable throughout.