Why not read our 100 best iPhone games ever feature
The Angry Birds series has been around since 2009. That's a fair old time in gaming terms, and a lifetime on the App Store. However, later instalments Angry Birds Seasons and Angry Birds Rio didn't change the gameplay formula much. They refined it, sure, but neither made as dramatic changes as Angry Birds Space.
However, Angry Birds Space remains a mix of the familiar and the new. A similar line-up of birds features, and those pigs are still there, under those blocks of wood, stone and metal. And you still fling one at the other using touchscreen gestures you'll have seen, if not done yourself.
The key difference is in Angry Birds Space's approach to gravity. This natural Newtonian force is at the core of any physics-based game - the original Angry Birds included - but this one gets to be more playful with it than most.
Levels aren't just made up of side-scrolling arrangements of small obstacles, but planetoids with their own gravity fields too. Each sphere's area of influence is shown visually, and - as in real-life physics - the centre of gravity is at the planet's core.
For the first dozen or so levels, the approach to gravity fields is easygoing. Rovio eases you into the difference between the vacuum of space and the pulling fields, and the notion of playing around a planet rather than along a plane is slowly introduced. This would become dull fairly quickly, but as design experts, Rovio's designers know when to tweak the formula - as a drip feed of new thrills.
Soon enough you're dealing with levels where gravity fields intersect, requiring more thought. And occasionally there's even such a conflict that a new centre of gravity between planetary bodies forms.
Before it all starts to sound a bit like Carl Sagan presents Angry Birds Space, we should say that the approach to gravity here is still very casual. It's based around consistent physics systems, but doesn't feel entirely precise - it's simplified, just as you'd expect from an Angry Birds game, or any casual game.
However, it does revitalise the arguably now-stale Angry Birds format, and enables a much more playful approach to level types. Occasionally, there's a near gravity-free level where you have to bash space detritus into space suit-wearing pigs, which ends up feeling like an interstellar game of pool.