If you're anything like me, the results of this simple algorithm leave you itching to go build an online Terragen, a jetpack-based first person shooter, fishing simulator, MMORPG, etc. This single-cube, canvas-projected demo practically begs for extension.
Here are a few things I challenge you to try:
Variation by height, where lower altitudes are smoother (like sand) and higher altitudes are more rocky
Cast shadows instead of purely slope-based shading
A second pass that generates caves and tunnels
Realistic terrain in 130 lines