Mysterio is such an iconic Spider-Man villain that it seems almost criminal that it took him so long to appear on film. That is why when he finally appeared in Spider-Man: Far From Home, it's tragic that Marvel and Sony missed the perfect opportunity. Ultimately, they did not use Mysterio well in Far From Home, even with potential right there in the source material.
In Far From Home, Quentin Beck is a disgruntled former Stark Industries employee who feels that his efforts were not appreciated and vowed to create a better "hero" than Tony Stark ever could. In isolation, Far From Home's Mysterio is a great villain with a clear motivation and solid origin in the Marvel Cinematic Universe. But it's just not as fun as Mysterio is in the comics.
It has varied across different stories, but the general idea is that Quentin Beck is a former special effects artist who worked in the movie industry. After getting fired from his job (usually because of Spider-Man), he uses his skills to create the illusion of Mysterio, a fake hero/villain made entirely out of "movie magic." He then tries to be a better hero than Spidey or his worst nightmare.
So, Mysterio is a character whose origin, motivation and abilities literally have the potential to be steeped in film history and rich movie references. And Marvel Studios and Sony used none of that for the character's first appearance in a film. It's hard to describe how huge of a missed opportunity that is.
Sure, it's a fun little nod that Mysterio's "real" costume in Far From Home gets revealed to be a standard motion-capture suit, and one scene acts as a pretty good riff on modern visual effects-heavy filmmaking. But those are references in isolation -- they don't get into the story or the characters. It's so preoccupied with being an MCU film slotted neatly into the universe that it doesn't realize it could have been so much more. Mysterio is just so extra in the comics, and in the movie, he's barely good enough.
Far From Home could have been a movie about making movies. It could have had so many nods and jokes related to Hollywood. There might have even been the chance to really interrogate how Marvel movies get made in a way that could have been meta and fun. All in all, Mysterio could have been such a fun, clever villain for the MCU. But alas, the powers that be never gave him the credit he deserved.