Minecraft is one of the most innovative games of the past decade. But it does get boring after a while of screwing around in it, and if you have next to no talent for building things in the game itself.
The bad. Of course minecraft doesn't have the best graphics, but the art style doesn't take away from the overall game itself. The soundtrack is lacking in the overworld, I usually just turn the music off and put on my own music on over the game. And as I said before. If you don't have a goal, then minecraft is pretty damn boring. You can set up projects like creating mansions or recreating things from popular culture or the real world, but if you can't build the things properly you can't really make them and you waste a lot of time making failed builds.
The good. Where as the over world is lacking in music, the nether, or underworld, has music that suits the feel that the nether gives off. The enemies are all pretty standard, with the exception of the things you find in the nether and the creeper. And it has a story, or goal, which is getting to the end and beating the Ender Dragon. The gameplay is smooth and the amount of creativity not only notch put into it, but allows the player to add, is amazing. Another good thing is that it is a time consumer. If you have to wait for something and you have nothing to do, this will take up the time that you need to fill.
Final Verdict:
The game itself costs about $21 for the latest version but you pay for the membership once and it is worth it. So yeah, I would suggest buying a membership.