Bloons TD 4

A large slate of levels and unique towers give Bloons TD 4 plenty of volume, but like an over-inflated balloon its content isn't substantial.

Despite its apparent expansiveness, this is lightweight tactics without the features and quality design critical to great gameplay.

The glimmer of in-depth tower defence is here, but a poor interface, unpolished level design, and half-hearted Game Center integration deflate the game before it has an opportunity to rise to the occasion.

Pop 'til you drop

Using an array of monkey-controlled defences, your goal in each of the game's 15 levels is to prevent waves of coloured balloons - cutely called 'bloons' - from reaching your off-screen base. Each balloon that bypasses your defences whittles down your lives from a starting total of 150. The bloons fly across the screen with startling speed, giving the game an energy that few tower defence titles can match.

Naturally, the colour of the bloons that fly across the screen dictates the type of defence needed to pop them. Simple red bloons can be popped with a basic dart-throwing monkey, though speedy purple bloons require stronger attacks from bombs or spikes to puncture the yellow, green, and blue bloons hidden inside. Bloons fill the map and dealing with the barrage is challenging to say the least.

Unfortunately, this impressive action deflates as the reality of the game's one-dimensional, unpolished design sets in.

Scatter-blooned

Foremost among the game's shortcomings is the interface, which is needlessly cluttered. Large icons for defences mean that adjacent units overlap. Moreover, upgrading units into bigger, more powerful forms often causes them to overlap adjacent defences. Add in airplanes that fly above the fray and selecting your towers becomes quite the challenge.

Not only is this visually confusing, but it also creates a problem when you try selecting specific towers. This overlap might be manageable on PC with the precision afforded by a mouse, but a fingertip is ill-suited for such a task. It's a simple issue that demonstrates the lack of attention to detail and poor optimisation for iPhone and iPod touch.

There are other control annoyances that stress this point. For instance, you can only set the target attack area for a mortar tower once. This seems reasonable until you upgrade a mortar for improved accuracy, which has the effect of shrinking the targeted area. Unless you placed its aim perfectly from the onset, your mortar fire may end up missing more bloons as a result of the upgrade.

Can't teach an old monkey new tricks

More problematic is the level design, which does little more than rehash outdated ideas. Lengthy levels drag on longer than necessary and oscillate wildly in difficulty - one wave might send a torrent of tough bloons, whereas the next is easily popped.

Not being told the makeup of the next wave adds to the difficulty. Rather than having the information needed for tactical planning, figuring out what towers to place is something of a guessing game. Unsurprisingly, this results in frequent failure and so the game devolves into annoying trial and error. A small box displaying the bloons coming in the next wave is enough to fix the issue.

Even the leaderboards haven't been handled well. Integration with Game Center is welcome, but the only way to access your high scores and achievements is through the Game Center app itself - there's no way of checking leaderboards from within the game.

Bloons TD 4 offers nothing new, content to stick with an ageing formula that has long been passed by more progressive titles. While not unplayable, it's a half-hearted effort that lacks the cleverness and attention to detail of a truly fun tower defence game.