I mean overall I was happy to attend. The costume theme was a bit lopsided. Apparently it was my BIL's idea and bride wasn't completely on board with it. I thought that she was based on the emails she was sending out months ahead of time but just before she said "it was A's idea" multiple times and I realized why when we saw the wedding party. The groom was dressed up in what I would call a Victorian type suit (my MIL made the jacket and vest) and all his groomsmen were dressed up as characters of their choice (there was Robin Hood, a character from a video game, Merlin, and I cannot remember what else) the bride was in an A line poofy bridal gown and bridesmaids were just in A Line gowns of different colors. There were probably about a dozen guests dressed up. I saw another Robin Hood, Mileficent, I was Melisandre from GOT and my daughter dressed up as a medieval elf.
I think everything would have been more smooth if they would have managed expectations better and asked questions. BIL was heard to say that he wasn't sure they actually saved any money by buying everything vs a company coming in and doing basic table cloths and flower centerpieces.
And yes they spent over 2 years planning this.