>>5464151HF (and all the sub lines like the super heroes, Chima figs and more or less parts of the Star Wars sets) relied heavily on the CCBS building system and had quite a lot of shells, bones and armor add-ons that often came and went.
It was mainly a pure construction line to show off the versatility of the new parts and system, with gear and action functions taking a backseat for most of the time or being relatively simple.
Meanwhile, Bionicle 15/16 seems to rely mostly on the most basic shells and bones (no engine blocks, Drilldozer armor, those trapezoid-shaped armors, etc.) while going back to more Technic-heavy builds and functions.
