Not a huge fan of Minecraft, but I can see the appeal for the LEGO/world-building enthusiasts.
People say this a lot.
I've already said that the game is probably my Game of the Generation, and its "lego/world building" aspects barely factor into the reasons why.
The real joy and immersion is in exploring, understanding and taming a wild world that's out to kill you every time the sun goes down. The first night in the game was for me, an intense experience of death, survival and hiding. Building a dirt hovel to hide from the night, eventually making an outpost of stone in the wilderness, and when I could finally survive the night, the exploration began.
Exploring the chasms under the sea, discovering collapsed sand dunes leading into buried rivers, bridging a magma-filled canyon with logs taken from burning forests, finding an underground lake infested with spiders protecting diamond, and emerging from a tunnel system into the belly of an ocean swimming to the top before the air runs out. The game combines an incredible procedural generation so its plains feel organic, considerable challenge and difficulty, and endless potential for exploration and eventual taming of the land from the hoardes.
The game completely absorbed me, as it does with others, and the heavily-mentioned lego-features are not always the reason why. Minecraft's atmosphere, in the right world and with the right player, can almost eclipse the atmosphere in nearly any big-budget game you'd care to mention.
That is indeed my opinion.