In Merged!, Gram Games developed what I consider to be one of the great modern puzzle games.

But that was a laid-back, calming experience.

As such, fans of Gram's previous output should be warned that its latest, Six! - trademark exclamation mark intact - falls somewhere between cerebral and twitchy.

Not two words you often hear together, right? Let me explain.

The title refers to the six sides of the hexagon you're responsible for shepherding down the screen, which sits upon a stack of snugly-packed, Tetris-style blocks.

Tap a block, and it disappears. The longer you can keep the hexagon atop the ever-reducing stack, without sending it tumbling off either edge, the higher a score you'll get.

Pause, think, tap like mad

On paper, it could hardly be simpler. But often, to most efficiently clear a path, you'll need to clear multiple blocks in a single move.

This is where your reflexes are taxed as well as your brain, as you race to clear four or five blocks before the hexagon clips one and spins off course.

In these moments, as you hurriedly and inelegantly unleash a flurry of taps on the screen, it could hardly feel further from your traditional puzzle game experience.

But quickly, you realise that neither quick fingers nor a wily strategic brain are enough on their own. To be good at Six!, you need a combination of both.

And in this sense, Six! is part of a great puzzling tradition. Think of Tetris as the stack gets perilously close the top of the screen, and you're desperately trying to find an L-shaped nook.

Or even Popcap's Zuma, when the balls start flooding in at a rate you can no longer handle, colours all jumbled up and no time to consider your next move.

Puzzle may be the genre most commonly associated with casual gaming, but that doesn't mean that it can't be just as tense, tough, and instinctive as any other. Six! proves this with aplomb.

Just enough

It's a simple idea, and one that Gram Games (rightly) chooses not to muck around with too much.

You've got your standard, high-score endless mode, as well as a series of shorter challenge stages - for those who can't bear the idea of a game that doesn't rank their performance out of three stars.

But it's more than enough. How often have we seen puzzlers with a glut of unnecessary modes, left largely unplayed and wasting space on the home screen?

Six! trusts its own mechanic enough to keep its package lean.

And when its flashier competitors have been discarded and forgotten, that tumbling hexagon will remain.