My biggest grievance with the new main menu is the color combination and the flashing right side sidebar (with scenarios etc.). The background is very dark and all the text and colors extremely bright, and I have my screen contrast + brightness already turned down way low to avoid headaches. Looking at the menu hurts my eyes and I don't want to make my screen even less bright or the game will look weird. The big mostly white "bubbles" on the right sidebar are switching in and out quite rapidly, and although this is intended to show more content, it's just annoying and also hurts the eyes. Minor grievance is that the household Sims aren't wearing all their clothes/hair. A lot of people use custom clothing and hair and those are not displayed, which kind of negates the point of having a nice big picture of your last played family.
Suggestion to fix: change the blue background back to the previous shade and brightness. Reduce large white areas floating on a dark background and flashing icons. Avoid white text on dark background for better readability and less ouchie.
The new design can trigger migraines and epilepsy. If it cannot be changed, at least give the users an option to revert back to old menu in the settings. It feels like the changes were made without sufficiently testing the new design, resulting in a "half-baked" product.