Welcome to The In-App Purchase Inspector - our regular look at free-to-play games from the consumer's perspective.

Each instalment, we'll be looking at the incentives or pressure applied to make in-app purchases, their perceived value, the expansion offered by the IAPs and the overall value of the experience.

The end goal will be to see whether the game makes a good enough case for us to part with our cash, or whether players are content - or engaged enough - to 'freeload'.

This week, we take a look at Rovio's free-to-play racer Angry Birds Go!.

First impressions

Who doesn't like a good kart racer? Mario Kart 7 was the first game I picked up for my 3DS, and I - like most gamers in my age group - can readily recall fond nights blasting friends with Blue Shells while zooming around Rainbow Road.

Now, Rovio's come about with a mobile take on the familiar kart racer and it's a simplified, and oh-so-mobile treat at first blush.

Controls are a basic tilt-or-tap affair, and each bird you choose to use has a special move like a speed boost or bubble zone they can use during a race.

There's no option to brake or accelerate, however, and this takes almost all of the strategy and difficulty out of races.

I saw 'almost' because Angry Birds Go! provides plenty of kart customization options to help each ramshackle buggy match your playstyle. If you're a bruiser on the course, you can upgrade your kart's strength while players who drive with more finesse will want to upgrade their kart's handling straightaway.

Each track has a series of challenges - basic laps, time challenges, versus, and the inevitable boss fight - so you get plenty of chances to familiarize yourself with a course as you go.

Finally, currency is split between coins - which you earn in game - and crystals, which are also found in game or unlocked via achievements or purchased.

Gaining purchase

As you might expect, you pay for your kart upgrades.

You pay with ubiquitous coins, which are showered upon you after you complete a challenge-– and you can buy a Coin Doubler ($6.99 / £4.99) to increase the rate that you earn this currency.

Each time you upgrade your kart, you up its overall size – which is measured, bizarrely, in engine displacement terms (cc). In order to race against bosses of every track but the first, you need to upgrade your kart until it meets certain cc requirements.

But coins aren't a premium currency - although you can buy crystals with hard cash.

The real incentive to spend on Angry Birds Go! comes via an energy mechanic which Rovio sneaks in after the first track. Each bird has a limited amount of stamina, and can only be used for five races before they need a lie down.

When they're exhausted, you can either wait until they recharge, or spend 10 crystals to bring them back into driving form immediately.

Considering that each boss needs to be raced against three times in order to be defeated - and, thus, recruited - it's easy to see you'll either need to swap birds (you gain more birds as you complete boss challenges), wait, or pay for crystals if you want to win.

Perceived value of in-app purchases

Overall, I saw good value in the IAPs in Angry Birds Go! - excepting for the constant rush to consume crystals.

There are a couple of premium karts on offer which run the gamut from $2.99 / £1.99 - $49.99 / £34.99. I'd definitely consider picking up the cheapest of these for its higher upgrade threshold and more appealing appearance.

The more expensive karts are not for me, however, and while there's no doubt they'd provide a huge boost to my in-game performance, I couldn't justify spending more than the cost of Mario Kart 7 (new) on a virtual buggy which I can't even apply brakes to in a given race.

Coming at Angry Birds Go! cold, I feel that Rovio really should have fleshed out its kart selection to provide a few more cheaper, incremental upgrades at the sub $9.99 / £6.99 point. This seems like a really basic step to help casually invested players become more invested.

The experience

Here's where Angry Birds Go! broke down for me.

After a player spends gobs of time - and perhaps gobs of money - on tricking our their ideal kart, their only real opponents to race against are quotidian green piggies and the episodic boss bird at the end of each level.

The kart racers that inspired Angry Birds Go! all provided players with a fleshed out roster of characters to race against and choose from, and while Go! eventually provides the latter as you recruit bosses, it completely falls down on the former.

Races began to feel very same-y to me in short order, and the lack of multiplayer - which Rovio will address soon - made me more hesitant to consider investing money into the Angry Birds racing machine.

More than that, however, the energy mechanic felt tacked on and perfunctory.

As a gamer that prefers their games without energy/fatigue mechanics, this provided a rather steep barrier to my enjoyment and investment in the game.

Overall value

...which is unfortunate, as there really is a lot to genuinely like in Angry Birds Go!.

I absolutely love the ability to collect coins and upgrade my karts between races, and would easily invest more time and money into this since it has immediate, and quantifiable, results on my kart's performance.

I'd even be tempted into buying the Coin Doubler as it plus the bottom-end premium kart would cost me about $10 all told and would set me up quite nicely for my time zooming around the brightly coloured tracks.

Given that these are not consumables and couldn't be lost in-game, there's a great amount of value to more invested players with both of these upgrades.

Conclusion

But being invested is the rub, and Angry Birds Go! struggled to keep my attention after a few hours.

As a matter of principle, I never pay to recharge stamina and energy gauges in games, and so the inevitable wait times between races in Go! pulled me out of the game entirely.

If Rovio tweaked its monetisation strategies, made coins scarcer, and relied on kart upgrades as the sole means of monetisation, I could easily see myself falling into a deep and casual love affair with Angry Birds Go!.

Sure, it's not a fully-fledged kart racer, but it's bright, fun, and a great experience to play when I don't feel like swapping out cartridges on my gaming handheld.

As it stands, it's a great glimpse at what might be - and I have every intention of revisiting it once the multiplayer is introduced to see if I can recapture the same excitement I felt on its early tracks.