Think tiny is the unstated guiding principle of the Ant-Man films, which ironically has helped it stand out from other areas of the Marvel Cinematic Universe that are more prone to the grandiose. 

The movie Ant-Man and the Wasp: Quantumania toy with that notion by shrinking Ant-Man/Scott Lange (Paul Rudd) and the other main characters to subatomic size ten minutes into the story and sending them to the Quantum Realm, which resembles James Cameron's Pandora as the cover of a 1970s jazz fusion album. 

They stay there for the remainder of the movie as they fight an exiled supervillain named Kang (Jonathan Majors). The end effect is a clever trick where the Ant-Man movie is both the biggest and tiniest.

Should I go see it? No, the middle hour is enjoyable in that trademark laid-back "Ant-Man" style. The Quantum Realm is like a psychedelic sci-fi cartoon version of those jungles in 1930s serials where a clueless Western explorer would misinterpret a gesture and annoy a local tribe, or get drenched in a river by an elephant, or be horrified by the idea of eating snake meat until they had a bite and realised it tastes kind of like chicken. 

Returning director Peyton Reed and screenwriter Jeff Loveness let the characters wander around the Quantum.

Here, the tribe consists of a man with a flashlight for a head and another with a transparent, gelatinous body who is fixated on the number of "holes" humans possess, as well as a telepath (William Jackson Harper) who is cursed to constantly hear the strange and/or impure thoughts that run through other people's heads. Instead of elephants, there are houses that resemble a cross between the Pillsbury Dough Boy and Fred Flintstone's house, are alive, can walk, and can fight for themselves in battle. 

Additionally, there are gelatinous insects and other animals, bushes and trees that resemble fungi and lichens, and a mitochondrial creature with Godzilla-like scales.

Kang is what fans of the genre refer to as a "ret-con." He's basically Thanos in a new disguise: a genocidal madman. Kang is a character that is poorly written; he is basically just bad, mad, smart, and desperate to leave the Quantum Realm. The actors and directors can only do so much to make him seem dreadful. 

The movie lacks the guts (or possibly the studio's approval?) to steal the audience's smile, like, for example, Avengers: Infinity Warlast’s act or Indiana Jones and the Temple of Doom's middle hour did.

The film eventually succumbs to the MCU pattern and spends the majority of its last act in too crowded CGI combat, with characters screaming that the universe must be saved while things collide, explode, and disintegrate. 

Sometimes the film overdoes the self-awareness in that horrible MCU way, as in this instance where a character declares another character to be awesome or confirms that something unusual just happened by commenting, "That was weird." The movie is saved by its low-stress, low-risk approach, though.

The Ant-Man movies appear content to be smart entertainments with heart, but not so much that they become cloying. They seem serenely unconcerned with expectations to set box office records or win Oscars. 

The series manages to be light but not insignificant, whether a particular scene is sentimental (anything involving Scott and Cassie) or cheerfully insane, thanks to the size jokes, running gags, and Rudd's casting, who has spent his career acting as if he's a random regular guy who stumbled into stardom and finds it all quite silly (the climatic fight at the end of the first movie atop a Thomas the Tank Engine train set).