The formal multiplayer takes the work ethic that defines the game, and then multiplies it. Since established servers have been running for so long uninterrupted, many have developed into sprawling mega-cities, rife with unique constructions and their own internal economy. It must have taken months and dozens of people working together to build these more complicated areas, and it's a testament of what the game can be when users work cooperatively.
It's too bad that after so much time, developer Mojang has still left multiplayer structure largely in the hands of the users. I appreciate the customization available, but simple features like a server browser, or easier steps to create your own quick game, would be appreciated. The game is constantly evolving, and I don't doubt that better multiplayer structure is coming at some point. Right now the process is simply too daunting for casual users, which means that some people will inevitably miss out on one of the most awe-inspiring parts of the game. Since the game has been such a success, perhaps crossing casual lines, this is an issue.
Sometimes Minecraft felt a bit like showing up late to a party. Like the complex structures that have been built brick-by-brick, the game has been iterating on itself repeatedly during its lifespan as an alpha and beta version. The learning curve might not have been so harsh if I'd been exploring from the beginning and learning new features as they came. The latest version is officially the 'finished' incarnation--hence our review--but Minecraft reads more like an MMO than anything else. Mojang has established a culture of constant updates, so the game's current state might be completely different within a year.
However many additions come, though, whatever new elements or mobs are put in place, the game itself has a strong core to rely on. It can be difficult and obtuse, slow and laborious, but that results in a rewarding sense of discovery and accomplishment. Sometimes work can be fun too.
Mining resources and crafting items from them are major parts of Minecraft, go figure.