Please, ponder with me the borders of hidden and emergent complexity.
By “emergent,” I mean “arising from interaction.” You can create incredibly complex designs with Legos, but the Legos themselves are simple. The complexity arises from the many ways you can arrange the simple pieces. There are, however, Legos that are cut into specific shapes for particular uses or that integrate unusual components like motors. Those have some inherent complexity.
In gaming, emergent complexity is generally a good thing. It is the source of the meta-game, and it is often what we mean by “easy to learn, hard to master.” The parts are simple, the whole is complex.
By “hidden,” I mean that the parts look simple but are themselves complex units. For example, PokÃ©mon catch rates can be very complex. For example, City of Heroes looked like it had a simple to-hit roll based on accuracy, but accuracy and defense were actually complex objects that could be decomposed by type of attack and of damage, so accuracy on a ranged psychic attack might be different than on a melee fire attack, and that was before modifiers specific to the skills, buffs, debuffs, enhancements, and inspirations. The latter string was emergent complexity (stacking simple modifiers), but the hidden complexity of how attacks were coded was the reason why the Vahzilok were devastating in the early game; there was no possible resistance against a few attacks that fell between those categories, and little in-game suggested it except the massive damage numbers that hit your hero.
In gaming, we sometimes like hidden depths. When something seems simple on the surface but hides complexity within, it can be like emergent complexity one level down. If you can analyze the situation to simple pieces forming complex wholes, we are back to the good situation above, with the bonus surprise that you can learn more than you expected. It can also lead to unnecessary complications and perverse, game-breaking interactions, encouraging players to focus on mechanical tricks rather than actually playing the game. (For some games, those mechanical tricks can become the game itself.)
You can see perhaps where I was with Reus when I learned that there were several levels of everything. Chicken + herd = rabbit is a simple thing, and many of those simple transformations gives us a complex web: emergent. If an unadvertised list of those transformations requires an unadvertised list of higher level versions, say I need greater chickens or a sublime herd aspect to even see that the higher tier animal exists,, and then I need a marginally advertised combination of ambassadors on my titans to unlock greater and sublime options, we no longer have an emergent system of simple pieces. The objects themselves are complex, and they do not decompose to simple pieces. Needing superior kangaroo rats to get a bull is coded into the game, not something that arises from intuition or interaction.
Gaming grognards tend to be rather okay with that sort of complexity too, as long as it is our complexity. Memorizing ridiculously complex systems and interactions is a rite of passage for becoming part of the in-group for the game, where the out-group slackers just refuse to learn which enemies are the placeholders for raid bosses and what their respawn times are. (At least a quarter of the reading audience will need to research EverQuest to get that one.) Knowing the hidden complexities is a source of power.