This suggestion might be asking a bit much, given it would require changing some core mechanics, but MineCraft should be more dynamic. There should be some creatures that modify the world around them, and more than those bomb-type creatures that only act when a player is in range. For instance, the Pig Men in the Nether might dig hovels or makeshift shelters. They would need to be restricted and localized, to keep them from continuously digging. There could be mole people, who dig complex tunnels, similar to the hive mind of fire ants, or a civilization that continuously builds higher in their city, restricted by resource needs. However, any of these would need to be restricted naturally to keep them from changing too much.
Another element for dynamism might be a physics engine. Have each block emit a downward vector, representing gravity; the blocks need to be able to redirect the vector, or crumble and be ejected randomly from a opening. If there is no opening, constant pressure could create stronger blocks. Other ideas would be to have conservative liquid mechanics, with a constant amount of water, or heat emitted from the bottom of the map and cold from the top. Erosion and other events caused on a micro scale could be represented by a random chance. However, these changes would cause a significant demand on the processor, with a much increased number of data values per block.
Another element for dynamism might be a physics engine. Have each block emit a downward vector, representing gravity; the blocks need to be able to redirect the vector, or crumble and be ejected randomly from a opening. If there is no opening, constant pressure could create stronger blocks. Other ideas would be to have conservative liquid mechanics, with a constant amount of water, or heat emitted from the bottom of the map and cold from the top. Erosion and other events caused on a micro scale could be represented by a random chance. However, these changes would cause a significant demand on the processor, with a much increased number of data values per block.