Just a quick note. I edited the sentence claiming that the "puzzliness" of Boulder Dash-type games is primarily a product of the number of types of object; this is not really true. It's true that in the BD series itself, and clones that take BD gameplay as a starting point, puzzle complexity is added by increasing the number of objects; but the Repton series, which has always had more puzzle emphasis than the BD series, achieves this with a far smaller number of objects (and not many added with each new game). The primary reason for this is that Repton's "spirit" and "cage" objects (introduced in the second game) are exceptionally versatile and, in combination with the games' other objects, can be used in so many ways that new types of puzzle using them are still being discovered.
Just a quick note. I edited the sentence claiming that the "puzzliness" of Boulder Dash-type games is primarily a product of the number of types of object; this is not really true. It's true that in the BD series itself, and clones that take BD gameplay as a starting point, puzzle complexity is added by increasing the number of objects; but the Repton series, which has always had more puzzle emphasis than the BD series, achieves this with a far smaller number of objects (and not many added with each new game). The primary reason for this is that Repton's "spirit" and "cage" objects (introduced in the second game) are exceptionally versatile and, in combination with the games' other objects, can be used in so many ways that new types of puzzle using them are still being discovered.