The question I get asked most about one shoulder dresses is whether they actually stay put, and the honest answer is that a good one does and a bad one spends the whole night giving you a reason to keep glancing down.
Where it falls short is anywhere you need to move freely without thinking about it. Dancing, carrying bags, sitting through a long dinner and reaching across the table for the bread, all of it tests the one shoulder construction in a way a normal neckline never has to deal with, and a cheap version with a flimsy strap or no understructure will slip, twist, or ride up at the worst moment. I learned this at a wedding in a dress that cost very little and looked wonderful standing still, and spent three hours doing that thing where you hitch the shoulder back up without anyone noticing, which nobody is fooled by, least of all the photographer. A proper one has a strap with actual width, some boning or an internal band at the bust, and fabric with enough structure to hold its own line instead of relying on you to keep adjusting it. On colour, solid shades are far easier to live with than anything busy, because the asymmetry already does a lot of visual work and a loud print fights with it. Deep jewel tones, black, and a good true red wear well across seasons and skin tones, while pale pastels show every mark and every faint bra outline you were trying to avoid in the first place. Satin and silk finishes photograph beautifully but crease if you so much as sit down for an hour, while a crepe or a ponte with a bit of weight to it holds its shape through a whole evening and travels folded in a bag without drama.
As for wear over time, the fabric is usually the first thing to tell on a dress like this. A cheap jersey or thin satin will go baggy at the one shoulder seam within a few wears, because that seam is carrying more weight than any other seam in the garment, and once it stretches the whole fit changes. A decent one keeps its line for years if you treat it properly, which mostly means hand washing or a cool gentle cycle in a bag, no tumble dryer, and hanging it by the hem rather than the strap so you are not slowly pulling the one point of the dress that cannot afford to stretch.
Given a few years of occasional wear and proper care, a well made one shoulder dress softens slightly at the seams, the fabric relaxes just enough to sit better on the body than it did new, and it keeps earning its place in a way the cheap version, long since stretched and binned, never got the chance to.