My honest opinion.
Quantumania is a fun, whacky, and ridiculously wild adventure. It's not 100% perfection, but it's definitely a great start to Phase 5, with a fantastic villain that sets the bar for a new dynasty. Overall, this movie is a worthy third chapter to the Ant Man story that deserves better praise.
Also, there was never any way to make a giant CGI head with little legs look convincing.