Taking to the Spanish Main with Glu's freemium sailorville Zombie Isle

Apple's App Store is littered with freemium titles, with hits like Smurfs' Village rivalling Angry Birds in terms of revenue. It isn't short of games involving pirates or zombies, either.

So it's strange that Zombie Isle is perhaps the first game to combine three of the most popular tropes on Apple's handheld device.

On first inspection, the similarities between Zombie Isle and Zynga's Facebook game Treasure Isle are very apparent.

Digging for treasure, using multiple tools, terrain with varying energy requirements, and food to increase energy are just some of the familiar features.

However, that's not all there is to this title.

As you can imagine from a title that revolves around pirates, the game involves undertaking a number of pirate-related jobs as you explore the seven seas. No self-respecting pirate would pass up the chance to partake in a little treasure hunting, and this is inevitably your main focus.

Treasure is grouped into themed collections, normally comprising four to five different items, and spread over various islands. Collections range from voodoo artifacts to zombie weaponry, which are made up from items such as candles, sickles, and voodoo dolls.

Completed collections can be traded in for experience points (EXP) and gold - the amount depending on the rarity of the treasure. When a set amount of EXP is reached, you will level up, increasing both your total energy and the number of islands you can access.

You can also unearth gold coins, keys that unlock chests and gates, and a variety of energy giving food stuffs.

Whilst digging, your energy decreases at a pre-determined rate. This is dependent on the harshness of the terrain, with coarse greenery naturally requiring more energy than soft sand. A simple spade will not suffice, with different terrains requiring different tools – a machete, or a hammer that must be purchased with gold coins, for example.

When your energy is fully depleted, you can no longer dig for treasure and are left with one of two options. You can either eat food - which will instantly replace a portion of you energy - or wait for it to replenish gradually over time.

There are numerous food types to be found in Zombie Isle, ranging from an array of fruit to uncooked meat – each with varying levels of replenishment.

Food is often discovered whilst digging, but never in amounts great enough to support a steady stream of activity. Therefore, it's inevitable that you will eventually have to stop digging and focus your efforts on other areas.

Upon leaving an island, you are presented with a top-down view of the world map, which is cloaked in a thick cloud of white and black.

You can sail through white cloud with your current ship, unveiling new islands and ports along the way. Black cloud, on the other hand, is impassable, at least until you can amass enough gold coins to purchase a bigger vessel.

Ports, unlike islands, hold no treasure, instead acting as recruitment centres for your crew of the walking undead. Once a port is reached, you must unleash a horde of 'hunter' zombies – the exact number depending on the port – with the aim of capturing it.

Once captured, further zombies must be used to infect its inhabitants before recruitment can begin. Each port houses a unique class of zombie, such as a Swordsman and a Shamen, and each has its own abilities.

Whilst sailing from one destination to another you'll occasionally see an enemy vessel, which are scattered throughout the seas. Your undead crew can now be put to the test in a fight to the death (again), resulting - if you are victorious – in extra EXP and gold.

Fighting is extremely simple and requires nothing more than a few taps – one tap to select your crew member and another to select his target. From there, the fight is an automated experience.

Although Zombie Isle is a freemium title at heart, you can play it to completion without spending a single coin. However, as with most entries in the freemium genre, spending money so will speed up your progress.

Alongside Zombie Isle's gold coin currency, which is earned in abundance throughout, a premium currency known as doubloons is also available. Doubloons are earned in very small amounts during your travels, but can also be acquired through in-app purchase.

Said doubloons can be spent on any number of items, ranging from improved ships, to packs of energy which allow longer periods of play time. Furthermore, doubloons can be used to purchase both common and zombie keys, or traded for a large quantity of gold coins.

Similarities with Zynga's Treasure Isle aside, Zombie Isle stands on its own two feet (or one foot and a peg leg). It contains enough content not present in the aforementioned title to feel like an original outing.

Early indications point towards a more balanced affair than previous freemium titles such as We Rule, which often only allowed small bursts of play - unless you were willing to pay real cash to speed things up.

That doesn't appear to be the case here as a multitude of activities can be undertaken.

For a first release, Zombie Isle packs lots of potential, with new levels and features already promised by Glu in future updates.