To me at least bionicle is about characters, and most lego themes aren't about the characters so much as the stuff the minifigs interact with such as vehicles and buildings, minifig creation is quite limited.
A lot could be told about a character with how a Constraction figure is built, in subtle ways, on the scale of a minifig thats a lot more difficult without making it obvious.
What can you tell me about zane from his design? he has angry eyebrows showing that he's determined, but pretty much all the ninja's have that, he has two swords and this armor thing, could that mean he attacks quickly? well again most of the time the ninja's use the same weapons, sure they have unique weapons but those are mostly just to be help differentiate them and mean little else.
But if we look at Kopaka, you can tell much more about him from how he's standing, his armoring, his weapons, and his mask.
His mask looks bleak and focused, not aggressive, but determined and focused.
His armoring is heavy, that could show that his personality is more guarded and reserved, his chest printing can also say something about his personality too, its (mostly) symmetric and organized.
And his weapons could mean that he has a defensive personality, the shield guarding him and his spear allowing him to attack from a distance.
You can take this same character theory and apply it to tahu and get something else, but with the ninjago characters thats a lot more difficult as they're all built nearly the same.
To me thats the best part of bionicle, the character theory, the personality in the figures, not whatever crazy looking vehicle they're driving.
Granted this can't be done to all of bionicle, it works on the toa Mata and most of the G2 sets really well but on some of the later G1 sets not so much.