I can give it a shot but it won't be an exhaustive list.
Lets start with the what we know and work backwards.
Certainly there is the technical aspect. This comes in two delicious flavors, concussive material (striking, kicking,blocking) and manipulative (redirection, subduing and throwing).
Moving back from WHAT a person does are the "HOW's. In this category are the manner in which techniques are done. A kata will often have odd little bits, seemingly pointless, sticking out around the edges. Often these are reminders to practice from a particularly unique vector or attitude.Also we dare not forget that though a nation can produce an art, there is always the matter tha different people will come up with alternate ways to accomplish the same thing. This is where one can get into stylistic differences.
Moving back yet again are the strategies. Most people are familiar with kata like "Bassai" and wonder at why some kata have such odd names. The names are often clues to the strategic or tactic approach one needs to take into consideration. For instance the idea or "theme" behind BASSAI ("to move from a position of disadvantage to advantage") is an art all in itself.
Moving back from strategy we come to philosophy. At this level a kata speaks to approach to the art or intention for training. For instance Itosu's development of the Pinan kata speaks to spoon feeding technical training to younger practitioners. Very different from the free forms of older training.In hand with philosophy are the health benefits. Best known are the TCC forms which are incredibly fine combat material when viewed through Chen TCC but also enhanced health exercises such as the Yang, Wu and Sun versions of the same material. BTW: For those who want to through Dim Mak into the mix I guess this would be the place to do it.
Lastly are the cultural bits such as breathing, poses, mudras, contemplation, dance, dress and so forth.
All of this stuff is just waiting there for people to discover it. All it takes is time and the desire to know more.