One thing that I try to emphasise to my game design students is that every design decision should support the explicit goals of their game; nothing should be implemented without first considering if a better, more conducive idea can be found or ensuring that the implementation does not contradict any other element. The player experience is paramount; everything should be in service to creating the kind of experience that you want to share with the player. Star Ocean: Integrity and Faithlessness exemplifies why this is an important thing to consider through a series of jarring inconsistencies and an over reliance on tropes.
Agar.io is ostensibly a micro-organism simulator. You play as a small dot and eat other small, static dots in the pursuit of growing bigger. But there are other mobile dots—other players—sharing your micro environment. Bigger dots can consume smaller dots. Communication between players is impossible. As much as Agar.io is about microbes, it also serves as a beautiful insight into human nature—and it’s an ugly little world.