It's been almost three years since Angry Birds first hit the scene. And since then, there have been numerous extensions to the game franchise, a flock of Angry Birds merchandise, toys, board games, wallpaper, pyjamas, all manner of tat. It's made Rovio very rich indeed.However, we've probably had enough of the adventures of the feathered crew now; it's time for the developer to deliver something new. Rovio needs to deliver the genuine sequel it's been promising for some time, rather than another, slightly rejigged take on the same theme.It's time for...Bad Piggies\nFormat\niPad (version tested), iPhone, iPod touch, Android\nPrice\n\u00a31.99, 69p (iPhone\/iPod touch), Free (Android - with adverts)\nWhere\niTunes\u00a0(iPad), iTunes (iPhone\/iPod touch), Google Play\u00a0(smartphone), Google Play (tablet)\nAngry Birds fans will instantly feel comfortable with Bad Piggies, the game starring the Birds' opposite numbers. The graphical style is identical, the menu system is familiar, and the tried and tested gameplay reward mechanic of\u00a0doling\u00a0out one, two or three stars depending on how each level is completed has taken over the casual gaming scene like a welcome virus.However, Bad Piggies is not Angry Birds. In fact, Bad Piggies has more in common with Rovio's other recent release, Amazing Alex, a game acquired by the firm (originally titled Casey's Contraptions) and tarted up before release.You see, the Bad Piggies themselves are on a mission to collect things rather than destroy them. They'd like the Angry Birds' eggs, but need maps to find them, and therefore the goal is to, er, get to the goal rather than rain down mass destruction.To do this, you must build a contraption that will help you traverse each level. At the beginning of a zone, you will be given numerous objects out of which to make the vehicle and must work out how they fit together best to not only get you to the finishing line on time, but also collect star crates and other pick-ups along the way.It sounds simple, but as the levels get harder, you get a greater number of items to build your craft out of. Some propel the construction, some help it fly, and some, such as the TNT, just blow things up and fire you into the sky. There is a lot of trial and error involved in Bad Piggies.And that's where some die-hard fans may be disappointed. While Angry Birds had a fair amount of trial and error to get perfect scores, it was actually quite intuitive to at least progress through a level with one or two stars. Bad Piggies is less forgiving. Get a cola bottle facing the wrong way, or a wheel attached in the wrong place and you have to go back to the drawing board.It is for this reason too that, unlike Angry Birds, Bad Piggies will be less appealing to kids. They can swipe their finger across a screen to fire a catapult, but constructing a five-box car with lemonade propellant, utilising clever but intricate physics along the way, will be too difficult to\u00a0achieve\u00a0for many children.That's not to say Bad Piggies isn't brilliant, it is, especially when you progress further. It's just not as marketable as the franchise that inspired it.