I think it's worth it.
There's two real flavors of Minecraft. Classic, in which you have an infinite supply of blocks and no mobs, is free on the website. You can just play it right there if you want. The latest release, Beta, is survival mode. In here you have nothing. You want wood? Cut down a tree. Stone? Mine it. Tools? Make them. Etc. Then there are monsters running around but they mostly only come out at night. There's no real set in place goal though besides not dying.
Some people like to explore. The world is procedurally generated so it's new every time and it maxes out at a total surface area equal to eight times the surface area of the Earth. So you can just pick a direction and head off and just see what's out there.
Then there's me, I like to build things. Right now I'm on a castle kick but I've got plans for a pyramid, a sandstone palace, and a huge tree fort down the line.
Some people like to build gadgets. There's stuff that functions like wiring in the game along with lots of other things. People have built some rather fascinating things. For instance there's the 73 cubic meters of TNT cannon I linked up thread. Another guy built a calculator out of game materials, other people have built sound synthesizers or musical arrangements. Rollercoasters and log flumes are also real popular.
Like the review in the first post says, Minecraft is largely what you make of it.
The graphics are pretty low res but the benefit of this is that you get an absolutely gigantic world to play in that can be randomly generated every time and can be run on most any computer.
So, on to some actual pictures.
First up, my current project. This is the first of my towers mostly complete, ie. monster proof. There's more work to do to make it look the way I want it to but functionally it's finished. For a sense of scale that tower is about 16 to 18 meters tall, I'd need to measure to be sure.
This is the courtyard. My original fort is contained entirely inside the new courtyard. I should be able to finish the last three towers sometime this week, depending on how my stone stockpile holds out, and once that's done this old fort is getting leveled.
This is the view outside my front door. That's a lavafall. This was just too good looking to make my base anywhere else.
Here's a good example of the kind of random terrain this game generates. This is about two kilometers from my castle.
And some more random scenery:
And some of the creepiest things in Minecraft, caves. This first one is about three kilometers northwest of my castle. It goes a long way down before petering out.
And this is the pothole from hell, a random hole in the ground. If you weren't watching where you were going you could fall in and depending on which side you fall in its deep enough to be lethal.