Ant-Man

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.

Fantastic Four

I had heard some pretty awful things about the new Fantastic Four, all of which were unfortunately true. Problem is, the characters were invented in 1961, the first movie came out in 2005 and the second one in 2007, so it's not like people didn't already know all about the premise of the show. The writers changed a few details. For instance, Sue Storm is adopted by an African-American dad, so her brother Johnny is also black. Doctor Doom in the comic is a combination scientist/sorcerer and ruler of an Eastern European country, here he's just a transformed thing that was once a person. 
An idea here is that instead of going into near outer space to gain their powers, they go to another dimension. It really bothered me that Sue worked on outfits with which the new dimension could be safely explored, but unlike with the actual Moon landings in real life, where we had a pretty good idea as to conditions up there, the characters here never send monitoring equipment on ahead, so no one had any idea of what conditions in the other dimension were like, so Sue is basically working in the dark. She has no idea what she's designing the suits to be able to guard against. 
I hate to use the word “cartoonish” to describe the villains in this, but it really fits. Very, very shallow, one-dimensional characters. Yeah, if I were writing this, I'd spend about 10 to 15 minutes on the origin and the rest on a real action thriller. They spend the entire movie just doing the origin.