Ant Man and Quantamania is not a movie but an example of movie studio which know that people will watch their movies no matter what, so just give them anything and they'll come to theaters with their tail wagging.
Movie starts with Cassie Lang making a device that can communicate with Quantum Realm and somehow the device malfunctions and our heroes get sucked inside the Quantum Realm.
Scott Lang, Hope Van Dyne, Hank Pym, Jannet and Cassie are sucked in Quantum Realm, but QR is a strange place which is inhabited by various creatures, and also Kang the Conquerer, a being who has lots of technology and control of time, who has a past with Jennet.
Who is Kang, what's his past with Jennet and how our Heroes deal with QR and its secrets is the plot.
Ant Man 3 is an Awful movie which has absolutely no charm of previous 2 Ant Man movies, Marvel sacrificed what made previous Ant Man movies good in order to increase the scale and stakes.
Problem of this movie is that the script is an absolute mess, Just like the Multiversal saga overall, anything is happening in movie and nothing matters, it can be confusing at times where you even think what exactly is happening on screen and why.
There are some jokes which land well but mostly it is a boring, even the action is monotonous and emotionless.
Writing in this movie is horrendous and some decisions taken are head scratching, there is an set piece in the end which if left as it is wpuld have created an emotional impact and would've built some anticipation for future, bye it is resolved abruptly and in one of the most ridiculous way, so we are left with neither emotions, nor any anticipation.
There is a subplot regarding rebellion which will make you remember Thor Ragnarok, and that's what this movie is for half of its runtime, Thor Ragnarok without any Entertainment, Emotions, Epicness.
Performances from leads are fine, Ant Man, Wasp, Jennet, Hank are all ok, but movie gives them not much to do, Cassie is something that actually does not resembles Cassie which you've seen in previous 2 Ant Man movies.
Man of the moment Kang The Conquerer is good, great even but certainly lacks the presence around him that Thanos had..... Yes he is showcased as much more dangerous than Thanos and makers want you to believe that he is but at the end movie itself undermines him.
There are some generic charcters from rebellion which makes you feel that they were rehects from Thor Ragnarok script, totally forgettable except one scene, and underdeveloped.
Mid and Post Credit Scene
If you think Movie undermined their next Thanos, wait for Mid Credit scene which looks less from MCU movie and more from a Zoo where bunch of Apes have been let loose.
Post credit scene is somewhat intriguing, bringing back a fan favorite, but just like all thing Multiverse, it's hard to be fully invested in it.
Final Words & Rating -
Ant Man & The Wasp is a complete mess and one of the worst movies from MCU, which lacks any entertainment or emotions and exits only to advertise next big bad of saga and the glimpse into the future, but not content with being a poor movie, even fails in being a proper advertisement.