If you have five spare minutes, Simon Sprint will fill them. Everything happens on one screen with patterns that speed up every level, down to 220 ms per flash, and the whole thing runs straight in the browser - no downloads, no sign-ups, no fuss.
Sound is part of the design - each pad has its own tone, and many players find they remember the melody of the sequence better than the colours. Turn the sound on once; you might be surprised how much it helps.
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.