Very happy that I saw Fantastic Four first and then Ant-Man, it was like going from canned tuna fish to broiled sea scallops, Ant-Man was WAY better! Not that the characters were really deep or complex, but both movies contained corporate villains that wanted to steal what the heroes had and make a profit off of it, but the Ant-Man villain was much less a routine, by-the-numbers bad guy and had at least some semblance of human-like motivations.
One of the founders of Marvel Comics, Stan Lee, usually makes a small cameo appearance in Marvel films. He didn't appear in the third Fantastic Four, but did appear in Ant-Man.
Special effects in both films were completely credible. The art of doing those has progressed enormously.