Version tested: iPhone
Last year, when discussing Kristan Reed's 10/10 review of Zookeeper FX Touch Edition, Oli suggested that "the next iteration is a shoo-in for our first 12". Thank goodness App of the Day doesn't require me to award a score, because I might just have had to disagree with him. Zookeeper Battle is excellent, but I'm not convinced it's worth more than an 11.
It is as it sounds: a competitive multiplayer version of the game Kristan rightly called "the world's most addictive riff on Bejeweled". This is the third time I've been caught in Zookeeper's grip and I'm still not entirely sure why it's so much better than the many other match-three games that do pretty much exactly the same thing. It's something that goes beyond the animals being chunkily adorable (even if they are) and the music being amazing (even though it is). There's some mystical alchemy at work, a special kind of digital magic that defies all logic and reason.
Whatever it is that makes Zookeeper great is back in abundance here. It's always been a game that thrives on simplicity, and sensibly developer Kiteretsu has opted for a brisk, no-fuss setup. Within 30 seconds you're up and running: you select an avatar and a username, and choose to play against random opponents or Game Center chums.
Matchmaking is pleasantly swift, and when an opponent is found, you have a choice of four preset messages to greet them with. It's a very Japanese conceit: the equivalent of a respectful bow before battle commences, and it's the first of many delightful touches.
"Just as often as you snatch defeat from the jaws of victory, you'll fluke a win through an incredible chain sparked by a generous cascade of perfect tiles."
Once you're in, you get half a minute to make as many matches as you can. Most animals count towards your attack stat, while elephants and hippos represent your defensive line. At the end of the round, your totals and those of your rival are totted up, the outcome of this numbers game displayed at the top of the screen, as the two animal avatars hurl glowing bolts at each other. Your energy bar will deplete if your opponent's attack figure is higher than your total defence and vice versa. The process repeats until one beast collapses. If both animals are still standing after five rounds, the one with the most remaining energy wins.
There's something oddly thrilling about seeing your chosen creature laying some serious smackdown - I defy you not to cheer them on - and equally, it's quite upsetting to see the poor fella take a pummelling. Among the most demoralising moments are those when you're on the verge of victory, and your opponent has been granted a power-up that sees his life bar partially refill, while yours is systematically demolished by a seemingly never-ending barrage.
Such caprice can seem unfair, but this is Zookeeper, after all. And just as often as you snatch defeat from the jaws of victory, you'll fluke a win through an incredible chain sparked by a generous cascade of perfect tiles, or the random appearance of the special panel that removes all animals of a single type. These elements of fortune are a way of allowing even Zookeeper novices to earn the occasional triumph, and are a boon for those of us whose reactions (and eyesight) have been dulled by the ravages of time.
The fact that it's free to download makes it even more essential, though there's one caveat: Zookeeper Battle has an energy system which restricts the number of consecutive games you can play. Now I'm fundamentally opposed to energy systems - or fun stoppers, as I call them - but this is the first I've come across since PopCap's Solitaire Blitz where I've been glad of it, if only so I can stop the damn thing taking over my life. Sure, there's a temptation to start another match immediately after the one you've just finished - whether it ended in frustrating defeat or joyous victory. But occasionally you'll have to wait for that meter to refill.
It's not as bad as it sounds. You can buy bottles (£2.99 for six and, bafflingly, £6.99 for 12) that replenish all six units, and you're given five for free at the outset. Download the game now and you'll benefit from a promotion that sets the wait time for a single game to just six minutes. So by the time you've finished two games you've got one back. Add your free bottles and even the most impatient player can play around 40 games before having to pay a penny.
You can also spend real-world money on inessential but helpful consumables that counter the new panels that occasionally show up. One sends the moustachioed zoo owner to your opponent's board to get in the way, while the other is truly horrible, splashing the display in mud so that all animals appear a dull grey colour. The items you buy simply negate the effects of these, while a third allows you to replace all panels when you're struggling to find a match. The latter sounds more useful than it is, as it costs you a couple of seconds while the screen refreshes, and you've no guarantee of getting a more favourable grid.
Besides a handful of simple unlockables, from new backgrounds to additional greetings, that's your lot. But what else could you possibly want? It's Zookeeper, it's brilliant, and it will almost certainly ruin your productivity for the next several weeks. In which case: you're welcome, and I'm sorry.
App of the Day highlights interesting games we're playing on the Android, iPad, iPhone and Windows Phone 7 mobile platforms, including post-release updates. If you want to see a particular app featured, drop us a line or suggest it in the comments. For daily app coverage, check out our sister site Modojo.