Thoughts on the movie itself
I really enjoyed Ant-Man. It didn't change the world of movie making forever. It didn't break the mould of superhero movies. It was still a really great, and fun, movie. I am particularly impressed by the way Marvel continues finding new ways to incorporate comedy into the films. This, I am sure, will continue to be Marvel's most notable attribute, the way they make their movies interesting and enjoyable for people of all ages, backgrounds, and superhero knowledge.
How it affects the MCU moving forward
Ant-Man wasn't Marvel's most notable film ever. It really wasn't supposed to be. I believe it was intended to open up the idea of masked and controversial heroes to Marvel's audiences. It seems to serve as a transitioning piece, from Tony Stark to heroes like Black Panther and Spider-Man. Ant-Man set up [Captain America: Civil War](tag:994409) rather well in that respect, allowing, once it comes out, audiences that aren't well versed in the Comics and history of Marvel to understand why the Super Hero Registration Act happens and is so controversial. Ant-Man is really Marvel's first foray into secret heroes. We also get a smidgen of information about what else is going on in the MCU at this point in time, the guerrilla writer at the end that mentions people who climb on walls is an obvious Spider-Man reference.
Ant-Man also, of course, sets up new heroes for the MCU in Ant-Man and Wasp.
I know know this was short, but Ant-Man was more of a filler than plot driver for the MCU. It served its purpose to show how masked heroes can come about and what else is going on in the MCU.
Let me know your thoughts, I'd love to expound on some of your ideas!