If you have five spare minutes, Fruit Storm will fill them. Everything happens on one screen with waves of 3-5 flying items with 12% bombs, and the whole thing runs straight in the browser - no downloads, no sign-ups, no fuss.
Swipes are free-form - a long slashing drag can catch three pieces of fruit in one motion, and that is how big combos happen. The gesture also has a cooldown per fruit, so waving the finger around randomly scores less than one committed slash.
Nothing here needs a tutorial or a wiki. Controls are one gesture, the goal is one sentence, and the difficulty comes from execution rather than homework. That is exactly what a browser game should be.