Arena 9

There's a huge dilemma for trading card game designers.

Make it too simple and players will get bored. Make it too complex and not enough players will spend the time learning the system for it to be commercially viable.

With its 3x3 grid, number-based trumping system, quirky character classes, and head-to-head gameplay, Arena 9, from developer Humble Gaming attempts to hit the sweet spot between the two extremes.

In its simplicity and tactical depth, the game manages to have the best of both worlds: however, it also retains the disadvantages of both simple and complex card games.

The simplest way to play is to lay down a card which has a higher number on one edge compared to the number on the touching edge of your opponent's already placed card. This turns the blue background of your opponent's card to your red colour, increasing your score by one.

You then take turns setting down cards until the grid is filled, with the person owning the most cards at the end of the game crowned the victor. The winner also nets more experience, which is required to level up, as well as Arena points, the in-game virtual currency used to acquire new card packs.

On its own, this would be too simple a mechanic to sustain long term gameplay. So there are other ways to win cards.

For example, if you lay down a card which results in two of its edges having matching numbers with the adjacent cards' edge (i.e. two 2s and two 5s) this is called mirroring, with both touching cards (if enemy ones) switching to red.

In addition, if any of those turned cards has an edge number which is higher than that of a touching edge on an opponent's card, it will also be turned over. In this way, you can get a ripple of secondary turnovers from a single move.

The other way of trumping cards, and triggering such effects, occurs during adding. This is when the numbers across any two edges add up to the same total - i.e. two and five across one edge, and three and four across another.

Again, both cards - if enemy ones - will be turned, with additional turnovers happening if numbers on the edges on the turned over cards are higher than adjacent edges.

Finally, each character has an elemental property, which is shown by a different edge colour. There are five in total, and in the manner of Paper, Scissors, Stone, you can perform elemental kills if you trap one element between two of its opposites.

As can be understood from such a lengthy explanation, Arena 9 packs a lot of tactical variation into each game -something that's heightened by random positions on some grids which provide boosts and debuffs based on elemental class.

Of course, aside from each bout, the main point of a trading card game is the way you build up your card library with rare cards or combinations of cards that support each other and your play style.

Arena 9 enables this in two ways. You can buy low rarity cards using Arena points earned playing against other players or the computer. You need wi-fi to connect with OpenFeint to be able to play online, although there is a head-to-head Bluetooth practice mode. This doesn't provide you with experience or arena points, though.

To gain the rarest cards you have to spend real money on packs costing either $1.99 or 99c depending on the quality of the cards offered.

The neat thing about the game is that while cards with high numbers are clearly more powerful, a skilled player can make do with a weaker hand. Your ability to turn over lots of cards late in the game means that everything can change on the final move.

Such openness also provides the game with its weakness. Since you always have to consider the cards currently on the grid and those still to play, it's easy to make a mistake that will see a winning position quickly melt away.

The elemental kill option is particularly tortuous as it contains no logic, nor has anything to do with numbers. Basically you either have to memorise it or physically note it down.

Still, with the number of experience points you have to rack up to reach the Expert level set at 3.6 million (you can buy your way in at a lower level for 99c if you want to), there's a strong incentive to keep playing if you want to unlock the top cards.

New characters are being planned to keep fans interested as well, although more social aspects such as tournaments and challenges will also have to rolled out if the game is to have a long term future.

Despite its openness, Arena 9 is quick to get into and you'll be forced to think fast. Even if it all goes wrong, don't worry - there's always another game starting soon.