The first principle of effective flag design is: Keep It Simple. Effective flags are meme-like, able to propagate themselves through human perception, memory, and action, and in this simple flags have an advantage.
On the other hand, there are certainly many highly complex flags. As the simplicity principle suggests, these tend to be obscure, expensive, and actually difficult to see should one come across them in use, up a flag pole. This isn’t to say they cannot be quite beautiful, when seen close up. Through the wonders of broadband, online media, and flag image repositories like Wikimedia Commons, we can easily access representations of these flags that let us zoom in and marvel at them.
Here are some examples. (Please do click on them to zoom in!)