While design can be "personal" there are some universal principles that can help you with your next project. I'm not trying to be personal here, as I think you did a great job! Some of these things are probably constraints from the homeowner, and a bit of it is my interpretation of design principles, so take it in the spirit it's offered please.
Lighting in a bath from over the mirror like that is harsher than if you had used sconces to either side of the mirrors. You've got the exposed bulb bottom casting glare and shadows. You still see a lot of sconces mounted on top of mirrors in older baths or retrofits, but many these days are changed to "uplights" bouncing light off of the ceiling to diffuse it's harshness.
You've got a lot of rectangular shapes here that don't relate well to each other. The mirrors, the two windows, the vanity bowls, the niche....they are all different sizes, and at different alignment heights. But, they aren't different enough for that to be a design feature, if you get what I'm saying here. Repetition of shapes is a good design principle to use, but when the elements aren't the same proportions, or alignment height, it makes it seem "off" and most people can't really tell you why it makes them slightly uneasy.
If you were to make a "feature" of the different sized rectangles, then some different sized rectangular accent tiles scattered here and there in the shower and floor to add to the asymmetry could have worked well, like a Mondrian painting. As is, I'd like to have seen more uniformity in the size and alignment. And perhaps some curves would have helped to relieve some of the tension in the not quite right rectangle look. Like oval mirrors. And some plumbing fixtures that weren't quite so hard edged and square as well.
And that brings me to the deco tile strip that you have running through the shower. (Gorgeous tile BTW!) It highlights the different heights of the square elements being off. And it's just a slash through the space, without being integrated into the rest of the design choices by perhaps continuing it as a chair rail around the room, or using it as the backsplash on the vanity wall. I would have preferred the niche be all of the deco tile, as well as have the strip be a bit smaller as there is something a bit off in the proportions of it's width as well. Or perhaps it's accented by the fact that it's such a contrasting element with the tile surrounding it. That contrast could have perhaps been used to frame some of those rectangles and create the illusion to fool the eye that you were dealing with similar size elements.
And just as a personal preference bit, nothing to do with "design", I prefer a toilet alcove to have tile behind that toilet, either as wainscotting or the whole alcove being done. It's just so much easier to clean!
