With the Marvel Cinematic Universe, flat visuals are an occasional problem. This problem has affected a few of the franchise's films and Ant-Man, in terms of the genuinely good MCU films, is probably the worst offender.
Ant-Man is a very fun and underappreciated superhero movie with a cracking script and some terrific performances, but the underwhelming cinematography is somewhat distracting throughout the film's run-time.
What makes it all even worse is that Edgar Wright was originally going to direct it and since he is a Brilliant visual stylist, this no doubt would've been one of the most visually striking MCU films had he not eventually departed the project (to the disappointment of just about everyone). Instead, Peyton Reed, a director of mediocre studio comedies, helmed the film.
Reed's direction isn't the worst ever; rather, it's just very uninteresting and one can't help but feel like he was out of his depth, since this isn't his normal genre at all.
Still, when he came back for the film's sequel, in spite of that film's overall mediocrity Peyton Reed's direction had improved quite a bit, indicating he'd found his footing in regards to directing outside of his normal genre.