My son got me started with Minecraft several years ago and I am definitely hooked! I am NOT a big gamer in any way, but the sandbox metaphor of Minecraft -- doing whatever interests you most -- building whatever you like -- keeps me going and always provides something new to do. I even went so far as to set up a multiplayer server here at the house (and now on a hosted server from MCProHosting.com) where my son and I, and some select friends can play in our own little world.
Minefull - My Minecraft Let's Play Video Series
You can download the client software and play in single player mode to try things out, but at just a little over $26, Minecraft is an inexpensive way to have a lot of fun with your computer -- in your own little world!