I don't really like the comparisons of this movie to the 66 Batman, because they don't really feel all that similar to me. They're both goofy, but they feel like different types of goofy to me. Maybe its because Batman & Robin feels more like a farce somehow, while Batman 66's goofiness feels more natural? Or maybe its because B&R's Robin is angsty and obnoxious, while a lot of the side stuff is just weird and lame (like basically everything with Batgirl, especially stuff like that waste of time race scene).
I don't think Batman & Robin is very good, but I watch it occasionally because it is the entertaining kind of bad, and its one of those "I had the VHS as a kid and watched it a lot" types of nostalgic movies for me. But, I think the biggest difference between B&R and Batman 66 for me is:
I genuinely like Batman 66, and I only get enjoyment from Batman & Robin because of how astonishingly bad it is. Those are very different types of entertainment.
The key was Season 1 & The Movie showrunner Lorenzo Semple Jr., who's 80s Flash Gordon movie was also really fun. Joel Schumacher and Akiva Goldsman are no Lorenzo Semple Jr.