As for Minecraft, I wouldn;t mind doing a few posts on it, but I'm of the opinion that it isn't truly a game. At least, Minecraft isn't a game by the technical definitions. It's definitely interactive entertainment, and it's definitely a video game (I do feel that not all Video Games are Games), but Minecraft is less a game and more a toy or a simulation with aspects of a game. Now, this opinion is based on beta, which is unbalanced and mostly elder game, but Minecraft is still a fantastic experience.
Gonna be all academic and pull out a quote for this...
"When you strip away all the genre differences, and the technological complexities, all games share four defining traits : a goal, rules, a feedback system,
and voluntary participation.
- Jane McGonigal ( her book Reality is Broken
Well, by this definition, Minecraft does have some work to do. It doesn't have a game imposed goal or ending, rather goals are imposed upon players by themselves in the form of exploration. It does have rules that you do have to follow, but they are very free-form.
Probably the thing that Minecraft lacks the most is a feedback system to go by. Right now, the score thing when you die doesn't work, so that can't be it. The only thing that could be a feedback system is just the self-gratification of a player creating something interesting; however, this isn't imposed by Minecraft.
And yeah, of course you are free to play Minecraft as you please. (Unless your addicted).
So yeah, as of right now, I am going to agree with Mat and say that it isn't technically a game YET.
With the addition of achievements, and Notch's apparently eventual goal of making an ending (this would add a goal for the player and then progress towards that goal would be the feedback system), I can see this turning into a true game, as defined by McGonigal
As of right now though, it is a very very very entertaining virtual sandbox.
On a related note, if you haven't read read that book that I quoted already, you really should. Its right up your alley Mat, as it validates our existence as game Designers.