Allow slideshow (or lightbox) arrows to be placed other than at the sides.
Allow back/forward arrows for slideshow (and lightbox) to fit not just at the sides of the slideshow but also right under the slideshow and not intrude on the image area. (Or maybe other locations too?)
And to be able to group the back/forward, thumbnails link, full screen button, and play button all neatly together under the slideshow.
And for these not to disappear/reappear or fade/unfade with mouse hoverings .
For example, from a page of another photographer:
(She does have mouse hover animation; but we can imagine that there's an option to allow the page designer to not have that.)
Meanwhile, with SmugMug, the back/forward arrows are on opposite sides of the content block and pushed to the every edge, which makes them harder to spot and requires more mousing by the user if the user wants to go back and forth sometimes.
Also, SmugMug forces a very slight animation (fading and unfading) on the arrows. And in the lightbox, the arrows appear/disappear depending on clicking on/off inside the image area. All that should be allowed to be turned off.
This is such a simple, basic thing.