Hmm,
thats an interesting topic 
I wouldnt call it “Difficulty” but maybe more like “Complexity”.
See, on one hand, you could drop in i.e. my AI from the TopDown Toolkit into your own project, set some aggro range/damage values and it works already. So it’s difficulty would be “Beginner”, right?
On the other hand, around half of my customers see the Toolkit as a learning resource, so they look at the features and how they are implemented and we are already “Advanced” now.
Great, so we now label it as “Advanced” (as some people mentioned). As a customer, how do you know if its difficulty is
- Advanced to use
or - Advanced to learn when dissecting
Also, with some assets the problem is that they contain more than one specific thing. Take the Topdown Toolkit or i.e. the Shooter Sample; Most of it may be very simple to use, but maybe there is just one thing inside thats already advanced to use. Is the whole asset now advanced?
Going further, maybe everything inside a package is really easy to use, but very advanced to be extended. I mean i.e. AI - you just need to drop the enemy into the level and he does his stuff, with some checkboxes and other values to drive his actions. Easy, right? But if you want to extend the logic, you suddenly need to know how to use the BehaviourTree and the state of the enemy in the correct context -> Advanced again.
So, to sum it up, i dont think its a good idea to have something like a difficulty-attribute customer-facing. Even if splitting it up into “Usage” and “Extendability” its never going to be right actually.
Cheers,