In a world filled with derivative grey zombie shooters, how do you make yours stand out from the shambling crowd. In the case of Madfinger's 2012 hit Dead Trigger, the answer was simple: make it look fantastic. However, though it was definitely one of the prettiest games on the App Store, it was let down by repetitive gameplay, dull enemies, and freemium grind fatigue.

With Dead Trigger 2, Madfinger has attempted to inject some variety into the series, adding new zombie types, more varied mission objectives, and a hideout featuring upgradeable workstations and weaponry. And, though there's no getting away from the fact that this is yet another zombie shooter, Dead Trigger 2 is an improvement on its predecessor.

Things start off in the US, where you are reintroduced to the zombie menace which is still threatening the world. Dead Trigger fans will immediately notice the new default control scheme, which does away with the fire button altogether. Instead, you need only to point your crosshairs at a zombie, and your weapon will discharge automatically

Though we did miss the satisfaction of lining up the perfect headshot and choosing when to pull the trigger, we found the ability to move, strafe, aim, and fire without ever lifting our thumbs off the screen incredibly useful, especially when heavily outnumbered. You can switch to the more traditional button-based system if you decide the autofire isn't for you, though.

The mission structure has also been re-jigged. Though the game still demands you kill a set number of zombies or survive while a clock counts down, these goals are disguised as sub-objectives in a larger mission. Now, you'll find yourself escorting team members to safety, firing up generators, locating water or fuel, and conducting research - all while pumping round after round into advancing deadites.

The story, which initially takes you across the US and Africa, is nothing more than a thin text-based thread used to string set pieces together. That said, with sniping missions, turret sections, and a host of new super-zombies - including the frenzied Rager and the radioactive Scienfist - the set pieces are more compelling than those found in Dead Trigger.

Of course, Dead Trigger 2 is a freemium game, and as such comes with the usual pair of virtual currencies. It'll also come as no surprise that it's still a grind to obtain the Gold needed to unlock advanced weapons and speed up the production of painkillers, grenades, and other gear.

Each of your workstations (medical, engineering, and so on) can be upgraded to improve their efficiency and output, but this process takes cash and time. However, to its credit, Dead Trigger 2 does not feature an energy system. This means you'll never find yourself locked out of the game waiting for a stamina bar to recharge. You will have to grind long and hard to collect the blueprints for weapons (which are dropped by random enemies) and the cash to build them, but at least you can do so without interruptions.

Like its progenitor, Dead Trigger 2 is still repetitive, grindy, and more than a little dumb. However, with more distinctive enemies, varied locations, and structured missions, it is a step up from Dead Trigger. It many not be enough to convince naysayers, but it should have fans of the original groaning in approval.