Another major twist is you control Ash, who acts as a hero unit. He auto-attacks whenever an enemy is within range, so you're only responsible for moving left and right, which is handled by tapping the appropriate side of the screen. There's also a selection of perk abilities, which you can call after a cooldown period. These include "Super Boomstick," a massive blast from Ash's shotgun, or "The Wrong Book," which sucks enemies into a swirling green vortex.
New perks are unlocked as you progress, though more powerful ones have slightly longer cooldown periods. Deciding which two perks to select has, at least in my experience, a bigger impact on gameplay than which troops you take into battle. It is tempting to grab two powerful ones, but with the longer cooldown periods, you may not get to use them as much.
Troop selection is a little disappointing. There's a decent number of normal and Hero units, each with their own special abilities. Yet, at times it can feel like you're just calling out whatever you can afford rather than a good counter to whatever is headed your way. There may be some sort of point-counterpoint system at play, but it isn't apparent. Since you know the basic makeup of the next wave, I would have preferred fewer enemies with a deeper level of strategy.
I also don't like that you're restricted to a 2D plane. It makes combat much easier, but takes away another strategic element. Choosing which lanes to defend would have added another much needed decision to gameplay and added new strategic options.
Army of Darkness Defense HD stumbles, but Backflip Studios did a great job at translating the license into a game. Fans will definitely dig what the game has to offer, and it may just create a few new ones as well.