It's a nice idea, but they're not the heroes Marvel needs right now
I've said it before but it bears repeating: I liked Ant-Man a lot more than I expected to. For a character I had zero emotional investment in, whose history in the comics is less than stellar, and a production that seemed disorganized from the outside, this movie didn't seem like it had a lot going for it. But it ended up being one of the better superhero movies this year. People expected it to flop, and it didn't. It makes sense for Marvel to try and take advantage of this surprise success.
Then again, up against the sh!tshow that was Fantastic Four and the convoluted mess that was Age of Ultron, the odds were actually in Ant-Man's favor. The plot was neither innovative nor impressive, but it was solid (proving that Marvel's predictable formula isn't bad in and of itself).
So: Why is adding a sequel a mistake?
Does Ant-Man have a strong, passionate following?
Not really. People saw the movie because it was fun, and because frankly it sucked less than the other summer action films released this year. It was kid-friendly, and there are plenty of gadgets and costumes that can easily be converted to marketable merchandise, but that's about it.
Does the character contribute to the universe in a meaningful way?
We'll have to wait until Civil War is released to know for sure, but in terms of character... not really. We have plenty of everyman characters already (Sam Wilson, Hawkeye, Colonel Rhodes) so Scott Lang isn't adding a useful perspective in that sense.
Does adding '& The Wasp' to the title compensate for the supreme failure to include any female representation in the Marvel universe?
Short answer: absolutely not.
Marvel is delaying the release of Captain Marvel
Just so they can fit a second Ant-Man film into their franchise. And while this will be the first time a female superhero will be getting her name in the title... eh? The first Ant-Man movie really *should* have been Ant-Man & The Wasp. Time and again over the course of the film Hope demonstrated that she was more prepared for the superheroics than Scott. She knew how to use the suit, she didn't need an extensive training montage to prepare, and she had a much more personal stake in the outcome.
Why should we settle for a character that the franchise barely seems to care about, when we could HAVE Captain Marvel?
She's incredibly popular despite extremely limited marketing because even though her solo film is literally years away fans are already excited. This is something we WANT. The Wasp in this last film was a teaser at best. At worst, it felt like everything we want but can't have for some reason was being dangled in front of us. "Oh, look at how cool and confident she is", "look at her suit, she definitely *could* be a superhero", oh wait never mind. This is an Ant-Man movie. So Hope got to sit on the sidelines while Scott took care of all the really dangerous stuff.
The Black Panther movie is getting pushed up.
The official release date is now February 16th, 2018 (It was previously July). Which is nice, but that feels like the only good news here. Marvel is reacting to the wrong things. Ant-Man's success is not a sign that they should pursue the character. It's a sign that they need to do a better job on their ensemble movies. Frankly, they need to be written better. No more half-assed character development, no more confusing plot holes, no more ignoring the previous films in favor of advertising films in the future.
Demands for a larger role for the Wasp are not a sign that they should turn her into Scott Lang's sidekick. It's a sign that fans are so tired of the minimal role of female characters that they're jumping on the most competently written one this year. Scarlet Witch? She seems cool, but we know almost nothing about her because Age of Ultron forgot to give her more character development after establishing that she loves her brother and hates Tony Stark. Black Widow? She was thrilling to watch in Winter Soldier but Age of Ultron might as well have undone all of that work with a ham-fisted romance subplot that managed to be both nonsensical and offensive.
It might sell Halloween costumes, but Ant-Man & The Wasp is no way to keep a franchise running.