There are five important aspects to a good layered dessert:
Obviously, the most important aspect is flavour. If your flavours are in flawless harmony, it won't matter how the other aspects are doing.
BUT if you want to give your dessert to anyone other than yourself or close family/friends, you'll need to pay attention to aesthetics. The old saying holds true; we eat with our eyes.
Taste and appearance are obvious aspects most people think of, but I find texture to be almost as important as flavour. Different textures in your dessert give contrast (though there should be contrast between your flavours as well), and keep your eating experience from getting boring once the basic flavours have been tasted.
For a more in-depth understanding of all this, I found this free (super short) baking textbook on plated pastry/desserts:
An example layered dessert breakdown:
Recipes from example dessert (for all diets):
I tweaked normal recipes to make every layer of this dessert low-carb and sugar-free. Click these links for the recipes.