Intelligently, the game gives you basic onscreen instructions during the first level, but in the levels after that it's up to you to work out the new rules for yourself. On the first try, you probably won't get them. There are always enemies to shoot, and shooting some of these enemies may or may not leave you with a glowing or pulsing dot to collect (more on these later). However, there's also usually some way of causing a chain of destruction that can clear large portions of the screen (and net you a lot of dots) if only you can work it out. The second time you reach a new level a bit of experimentation will probably give you some more idea of what to do, and after the third or fourth time it's just a case of doing it. With dozens of enemies and an inordinate quantity of bullets knocking around the screen at any time, this can be harder than it sounds. Luckily your ship is extremely agile, particularly if you bear in mind that it moves faster when you're not firing.
Taken on its own, each Riff level is an elegantly constructed little shooter, full of clever mechanics and a great mix of memorable patterns you can work with, and random elements that keep it unpredictable and interesting. As a result, the game is immensely enjoyable and hideously addictive. However, while Riff kicks off with a fairly gentle learning curve, it does get tricky once you're on the third stage and beyond. As you have to go through each level in turn in the main single-player game, this might be a drawback for those of us who aren't hardcore shoot-em-up fanatics.
Luckily, the game has an elegant solution built in. Remember those dots you collect? Well, at the end of each game all the dots collected are added to a central running total, and from there they can be used as credits to buy additional lives, taking your starting total from 2 to 3 to 4 if necessary. Collect 200 or 700 dots in-game and you'll also be rewarded with an extra life. What's more, lives aren't all you can buy with the dots. You can unlock particular levels as ‘singles', giving you the chance to play and practice them without having to work through their predecessors first. Once that's done, you can also unlock shuffle mode, so that the game shuffles your available levels each time you play. As a result, Riff is satisfyingly tough but also quite welcoming provided you're prepared to play enough to meet it halfway. On top of this, dots can also be spent on new colour treatments and visual effects - a bit like the optional visual schemes in Rez.