So what's so great about lunges? Apart from the fact that it works multiple muscles it's also a one leg at a time, training one side of your body independantly for the other hence improving balance and coordination. Lunges (in good form) also increase hip flexor flexibility and improves the glute activation, as the position isolates and activates the glutes. When keeping your spine upright you also improve that all important core stability!
Have a look below to see some good quality lunges.