Released at a time when puzzle games were flooding the market, Dr. Mario stands out as one of the best, combining a smooth learning curve, playful graphics and memorable tunes. Mario tosses vitamin capsules made of red, yellow and blue halves into a bottle filled with viruses of the same three colors. It's up to you to rotate and move the capsules into place to clear the bottle of these nasty creatures. Viruses and capsules disappear when four of the same color are aligned either vertically or horizontally. The fundamental concepts may be simple, but the addictive gameplay becomes progressively more complex as the speed increases and additional viruses are added.