Sign away your life, stock up on hot pockets and red bull, lock the doors, and over feed the cats.. its time to play MC!
There is so much depth to this game that I cannot possibly explain it all in a singular way. There are a few game modes, from survival to hard core that give players a different experience each time. Your world is endless, say for the upper and lower height limits of 128 blocks. 64 blocks above ground and 64 blocks below. There are caves, canyons, mountains, valleys hills, open deserts, oceans, and vast underground strong holds to be explored. Resources from wood to Diamonds, (Oh God'da love those diamonds) must be gathered and used in order to survive in survival mode.
In creative mod you don't have to worry about resources as they are all right there for you to add to your inventory. You can build anything that your mind can imagine in this game. Albeit, it'll have to be done in squares. :D
Great game for kids of all ages. Excellent concept, execution, and support. Awesome community with literally thousands of videos, tutorials, mods, skins, files, and world saves.
Be warned though, once you start playing you'll forget about everything else. Better get that I.V. started before you log in for the first time.