The best ideas, of course, are the simplest ones and Vorble's core idea is deliciously simple. It's what developer MegaTree calls a "mind sport", a three-dimensional spin on chequers with maybe a bit of backgammon and dominoes thrown in. Play takes place on a sphere made up of geometric faces - some pentagons, some hexagons. It's like a football, a fact the tutorial handily illustrates by temporarily changing the colour of the faces to black and white.
Changing the colour is also what you'll be trying to do, by placing pegs on these five and six-sided panels. Once a panel has as many pegs as it does sides, a cascade is triggered and those pegs are sent to the surrounding panels, leaving the original panel clear. If your opponent has placed a peg on a panel, the only way to take it off them is by catching it in a cascade. As it's played on a sphere, there's no boundary to the game and triggering chains of cascades that keep going around the play area is where the big scores lie, and as the "board" starts to fill up with pegs, the potential for a game-winning avalanche increases.
It's one of those ideas that seems so compact and perfectly self-contained, and so obvious once you've seen it in action, that you wonder why nobody did it before.
Vorble taps into the sort of time-worn strategy that propels most classic board games, but has enough of a twist that relying on tactics from those pastimes won't get you very far. In the space of just a few games, you start to get a feel for its unique rhythm. Taking control of the pentagons is an obvious priority, as they can reach cascades one move faster. How you build up the hexagons nearby is often the key to success, as you become uncomfortably aware that each peg you place can be turned against you by a well-planned cascade.
Vorble impresses in ways beyond the clarity of its concept, though. The single player mode is more demanding than most, since it uses AI rivals who have been "evolved" over thousands of generations, programmed with the rules and running automated games until interesting "personalities" were detected. It's just a shame these intriguing competitors are represented in-game by chintzy stock photos of monkeys and fairies, as they leave the game looking a little tacky.
Online multiplayer is well handled, with friends list support, live chat and four game modes: Classic, Loaded, Speed and Chaos. Diving into a public match with a random player offers only Classic play, but it's smooth and fast. You can also take turns playing on the same screen. Rather brilliantly, stats from every match played get uploaded to the Vorble website, so you can not only follow the leaderboards but watch an interactive replay of every match ever played by every player. It's pretty staggering stuff, the sort of deep community feature we've come to expect from AAA console juggernauts like Call of Duty or Halo, not an indie iPhone game.
In the end, though, it all comes back to the simplicity. The creaky old idiom about something being easy to learn but difficult to master may be a cliché, but it sums up Vorble perfectly. That there are still brilliant little ideas like this waiting to be realised is reassuring in a gaming landscape where repetition has become the norm.
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