Try to memorize the serie of illuminated keys and reproduce it, at each step a new key is added to the serie and the game becomes more difficult. In the level 3, there is 6 light keys, and speed game is faster. If you want an original Simon game, this game is ideal for you.
The Simon Game level 3 on this website is totally free, it's a good memory trainning, you play as many times as you like. The serie is randomly generated so the game is unlimited.