In larger pieces that I attempt, the images seem to have very good moments arranged in not altogether pleasing ways. To be fair, glitter pens do not photograph well; this tile looks lots prettier in person (in paper?) than digitally. Still, it seems to be true that Zentangle tiles that are somewhat tedious to draw are often the ones that look the best as finished pieces. In other words, one simple design seems to be what the eye hungers for, and if complexity is your thing, it helps to frame it in a very regular, overall design.
I'm still casting about for my voice in this medium. The Zentangle method offers a wealth of many useful designs and techniques, but these are best applied with clear intentions. Local focus needs to work in harmony with a broader vision. I am comfortable with local focus; the broader vision part is a bit harder to grasp.