Tiny Invaders, the first iOS effort from independent UK studio Hogrocket, cleverly subverts the staple iOS cutesy aesthetic - most of its cast are nothing short of adorable - to propel you into a puzzle game about microscopic aliens burrowing into human bodies and infecting their insides. The end goal? To crush the human race and take over planet Earth, naturally. Which is just lovely.

At its core, Tiny Invaders is really a railroad management game, with the adorable parasitic alien lifeforms taking the role of the trains, the track supplied by gooey internal organs. The unique visual identity ensures the game has its own distinct look, and the organic context means path designs aren't restricted to overlapping right angles.

It's also particularly refreshing to see that Hogrocket doesn't spend too long fussing over a procession of simplistic tutorial stages, instead treating the player with enough respect to have the difficulty ramp up to a respectable level in the first few stages. Four batches of 15 levels are present in the initial release - with more promised for the future - and getting three stars in all of them is challenging and meticulous work.

At least, that's if you want to get the three-star rating for each level. If you're not fussed about that then the game is simply a complete doddle, as there's absolutely no way to fail - lose your little parasites and they'll simply respawn from a grinning hive creature. It would have been much preferable to have seen more of a harmony between the needs to cater towards casual and challenging interests simultaneously.

Your only enemy in the early levels is the clock, but later levels open up additional challenges such as white blood cells and choke points that force you to speed up. You'll also have to handle the manual switching of tracks throughout the game, which requires both planning and precision, as many of the stages criss-cross into various confusing shapes.

Sadly, however, with so much going on the game can become slightly overwrought and fiddly, especially when you're trying to juggle your invaders' speed boosts while handling myriad switching paths. Seeing as how the timing for three stars is quite strict, one accidental input is often more than enough to throw you off kilter, and when that happens two or three times in a row it takes away some of the sheen.

Hogrocket's iOS debut has managed to set up a great premise, but the promising development team hasn't quite been able to deliver the goods. Ultimately, Tiny Invaders fails to build upon its entertaining concept.