I say forgettable, because not even a week after seeing it, I cannot remember much about the movie. I had the same problem with the first "Ant-Man," which I did not like as much as this one. I knew what I was going into with this movie. Something a little smaller scale (no pun intended), a meh villain, and plenty of humor. This movie delivers and takes some of the best jokes from the last movie and brings them back, strengthening it.
Spoilers abound people!
The story revolves around Hank Pym (the original Ant-man) finding his wife who disappeared in the Quantum Realm, which we learned in the first one. Hank and his daughter believe they found a way to get back to her but not without the help of our titular character. The flow of everything seems natural, nothing seemed out of place and forced. The story is a decent one, however, it is forgettable. The only thing you'll remember is the end credits scene. Hank, his wife Janet, and their daughter Hope have all fallen victim to the snap of Thanos. Thus bringing Ant-Man to "Avengers 4." The post-credits (at the end of the credits), has a silent world surrounding an over-sized ant playing the drums.
The humor is great. Luis gets a scene where he tells one of his famous stories, which was one of, if not the best, part of the movie. Paul Rudd writes jokes in this that flow and are incredibly funny, however, there are a few times that the humor interrupts a sentimental scene. The CGI is good for the most part, however, there are a few moments where it falls flat. Music is forgettable, I have no idea what kind of tune they played.
The villain is the most interesting part of the movie. It isn't about someone trying to take over the world or spread corruption throughout the nation. It's about one woman's goal of survival. Yes, she interferes with the plans of our heroes, but she isn't a villain. She has days to live because of Pym's experiments and is desperate to find a cure to her condition. The cure comes of "Deus Ex Machina", which essentially means that the solution comes at the last minute out of the blue. When you think about it, you tend to believe or understand that you would do anything in order to live another day. Why leave everything you worked so hard for when you have a chance to continue building and experiencing life?
All in all, "Ant-Man" is a movie all Marvel fans should see in the theater, to have that experience. To the average movie-goer, I'd highly recommend either skipping it or renting it if you really want to see it. Regardless, I believe you will have fun with the movie, but you won't remember much of it after a week.