When Rovio boss Peter Vesterbacka said that Angry Birds was going to follow the same template as the Mario franchise, I didn't realise he meant it quite so literally.

Following a brief trip into outer space, a cartoon series, and a go-kart racer, we now have a cute RPG. I'm hoping for Angry Birds Golf next.

You shouldn't except anything quite like Paper Mario here though. Angry Birds Epic has no towns, civilians, or side quests. And the story isn't a legendary tale of cataclysmic events, amnesic heroes, and a 'chosen one'.

The game is just a non-stop procession of fights you pick from a map. You do all your shopping from a dedicated store screen, and the nonsense story has something to do with birds and pigs. And eggs.

Dragon Nest

The combat appears simple at first. You can drag a bird onto a pig to attack, tap on a bird to do a defensive move, or drag a bird onto an ally to buff their stats. Oh, and there's a hot chilli pepper that activates a special move.

But this straightforward and streamlined set-up actually hides a surprising amount of depth.

There's a huge bestiary of different swine baddies to fight. They can charge big attacks, throw up a smoke screen, target specific birds, resurrect fallen allies, or call more pigs onto the battlefield.

There are status effects, like poison and sleep, you can craft new weapons and shields and use loot to brew potions, and the birds can hop between different classes (and change their move set) by swapping head gear.

The constant barrage of battles gets tiring, but the fights are fun and - more than most RPGs - juggling your small toolbox of attacks, spells, and items to defeat an enemy almost feels like solving a puzzle.

While it can feel simple and repetitive when you're stuck with one or two birds, things really open up when you have a whole crew of avian warriors to choose from.

Chuck in Matilda the white bird cleric, and Chuck the yellow bird mage, and things start to get interesting.

Chrono Pig-ger

But all of that is, predictably, undermined by a persistent, nagging, and manipulative demand to spend money or watch video adverts.

You can pay for potions, watch an advert to boost your attack power, spend money to resurrect downed birds, and drop cash into a tombola to win legendary items.

When you craft, the item's base stats change on the outcome of a die roll. And when you finish a level, your loot is determined by a roulette wheel. In both cases, you can pay to re-roll or re-spin, adding a pernicious pinch of luck and gambling.

This all boils down to one simple fact - if you don't pay up, you're going to find the game much tougher.

You'll face a fair amount of back-tracking, enemies will be harder to defeat, and crafting items harder to come by. It won't be long before you're blaming every death on the invisible hand of Rovio.

But, for what it's worth, grinding has been a part of RPGs since the 8-bit era. And I haven't paid a penny (though I have watched a few adverts), and I've found the challenge just right.

But those new to the genre may find themselves hitting a brick wall until they fork over a few golden snoutlings or watch an hour's worth of ads.

Swine-al Fantasy

Angry Birds Epic is a surprise. It's cartoony, casual, and unmistakably free-to-play, but unlike most games that fit that profile, Rovio's RPG has depth, challenge, and lots of unique content.

The lack of exploration and the endless IAPs will infuriate Dragon Quest and Final Fantasy fans, but if you want to try out this genre and (crucially) you don't want to pay for the privilege, Angry Birds Epic offers up a pretty comprehensive intro to RPG basics.