Glu is a master of the free-to-play arena, having released many games that offer no barrier to entry but constantly pepper the player with requests to spend real-world cash on in-game items and currency.

The studio has honed this approach with Frontline Commando 2.

By that, we don't mean that it has finally created the perfect freemium experience. Nope, we actually mean that this title is sure to be incredibly profitable for its creator while annoying seasoned players.

Weapons can be upgraded, but expect to pay real cash to get the best firearms

Taking visual cues from Activision's Call of Duty series, Frontline Commando 2 represents a considerable visual upgrade from the original game.

Characters are detailed and environments packed with complexity - which just about makes up for the fact that you can't navigate them freely. Instead, you are forced to adhere to pre-determined points of cover.

You can pop in and out of cover with the tap of a virtual button. You use another button to control your weapon. You aim using the touchscreen, and swipe to move your crosshairs.

From time to time, you'll have to deal with enemies that are way off in the distance - this usually means switching to a longer-range gun, such as a sniper rifle. Occasionally, there's the chance to switch position, usually when your current form of cover is under unstoppable attack.

The core gameplay is fast, fun, and hugely enjoyable (even more so when you introduce AI-controlled buddies to assist with the wholesale slaughter). However, the fun only lasts for so long. Sooner rather than later, you see, you'll be poked and prodded with the dreaded IAP stick.

Your AI partners can help to distract enemies, giving you the chance to hit back

While Glu dishes out gold and cash - two currencies used to purchase weapons, acquire upgrades, and train your partners - fairly regularly, it soon becomes obvious that you'll need to dip into your pocket here in order to maintain pace with the game.

Glu is keen to remind you of this fact at every available opportunity. Before boss battles, for example, a message helpfully pops up that states you should probably think about improving your equipment, which - you guessed it - revolves around spending real money.

Despite this, the solo mode remains entertaining, thanks to the pick-up-and-play mechanics and generally excellent presentation. Multiplayer is also included, but it's not as involved as you might think (instead of fighting the other person in real time, you are actually taking down her AI-controlled soldiers).

Frontline Commando 2 is yet another example of how free-to-play can work - marrying this business model with amazing visuals and enjoyable shooting action will almost certainly result in plenty of players splashing the cash.

However, those who prefer to pay a one-off entry fee and not have IAPs paraded in front of them every few minutes might find it harder to appreciate.