At first glance it would be easy to accuse social gaming giant King of resting on its laurels with Bubble Witch Saga 2. Dig deeper, however, and you find that the orb-launching match-three formula has received a tweak or two for its second outing.

The most obvious change is the improved visual design. Gone are the moody stills of three hag-like witches, replaced instead by vivid backgrounds and the cheerful Stella, who looks a bit like Barbie in a pointy hat.

While the new visuals pop, the old gameplay remains intact. You're still bursting groups of coloured bubbles by shooting them with orbs of the same colour. However, a host of small additions improve the game for both newcomers and returning fans.

Many of these changes are subtle, but serve to make the game more intuitive. A narrower playfield makes the action more fast paced. An upgraded guideline shows whether a shot is blocked, while also providing a handy indicator of the bubble’s trajectory after its first bounce. This helps you make tricky shots to erase bubbles at the top of a stack, causing a satisfying cascade of colour to come raining down.

The biggest improvement to the original comes in the form of new goals. Along with the classic screen-clearing objectives, some levels now demand you clear specific creature-filled balloons, while others have you trying to release ghosts that are trapped on all sides by bubbles.

These ghost levels are particularly neat. The spirit acts as a pivot for the spheres around it. Any impact spins the bubble-structure around its ghoulish axis, helping or hindering your next shot depending on the angle. Its a nice twist that makes planning your shots even more important.

As is so often the case with free-to-play titles, Bubble Witch Saga 2’s IAPs ultimately sour the experience. Every time you fail a stage, you can't shake the feeling that the game gave you fewer bubbles then needed to force you to purchase more.

Bubble Witch Saga 2 is undeniably derivative, but this doesn’t stop it being a solid match-three puzzler. Were it less aggressive with its in-app purchases, and didn't feel like it was deliberately sabotaging your success, then we would feel more kindly towards it. It's a step up on the original, but second-guessing the IAPs spoils the fun.