Exactly, feels like only yesterday that Queen Victoria was sauntering up the aisle!
I think it's borderline OP. And borderline in a couple of respects. Borderline too cream because, despite having a lot of patches of colour, something about the design leaves it feeling like a cream/white dress. I guess those cream bits define the structure.
I also think it is possibly borderline in terms of formality, depending on the wedding. As others have said, it looks essentially like a sundress, and I don't think it will carry a warmer layer well. Many are the dresses ruined by having to put a badly accessorised cardigan, jacket or wrap over it to allow for a rainy day.
In summary, I would not be aghast if I saw you in that at a wedding but truthfully I might lazily think "Some people are going to think she chose poorly." What I wouldn't think is "What a well-chosen outfit."