As usual, the folks at Marvel Studios know what they're doing. If you've enjoyed all of the other Avengers-related movies, you'll probably like this one as well. You have good characterizations for the hero and his supporting cast, and there are plenty of great action scenes that get supplemented with some special effects that feel pretty fresh. (That's probably the one thing that this movie really has going for it.) You'll also get carefully placed references to the other movies and the greater Marvel Universe that aren't distracting for the non-superfans but get us comic geeks pretty excited.
Anyway, there really isn't much that I can say that they did wrong. Some of the comic relief bordered on being a bit much, but just when I worried that it was going to be over-the-top, they reigned it in a little. With that said, here are some random thoughts:
Paul Rudd - Casting Rudd as the Scott Lang version of Ant-Man was a good start. He's a charismatic actor, and while he normally does comedy, he's believable as an everyman action hero. I've always liked him, and he's probably the key reason why I Love You, Man is one of my favorite comedies.
Hank Pym Versus Scott Lang - The movie takes a lot of liberties with the story of Hank Pym, the original Ant-Man, but it's clear that the screenwriters were well-versed in their Marvel Comics mythology. Even if certain characters and events didn't happen exactly the same way as they did in the comics, there were plenty of references to keep fans happy. (In other words, fans of The Wasp won't be completely disappointed.) As for Scott Lang's character, I've been reading the recent Ant-Man series (which is really good) and it really rang true to me. He's a former crook with a heart of gold, and he wants to do right by his daughter. Excellent.
Evangeline Lily - There's a lot of talk about how these superhero movies treat their female characters, and no doubt some people will wish that she could have had a greater role. Still, I think that she serves a definite purpose in the story, and she's hardly a generic love interest. Also, a pretty solid reason is given why she doesn't strap on a shrinking suit herself. Hopefully there will be a sequel, as there is hope that she'll get to do even more. (Or maybe even in the next Avengers movie.)
More Ant-Man in other movies - Again, hiring Paul Rudd was a good choice. He'll definitely present an interesting dynamic with all of the other assembled Avengers. I'd really like to see him interact with Robert Downey, Jr.'s Tony Stark.
So, there ya have it. If you are familiar with what superhero movies come specifically from Marvel Studios (as opposed to originating in Marvel Comics) then you probably have a pretty good idea of what to expect. If you've liked all of the others, you'll no doubt like this one as well. As to whether you rank it as a lesser or greater entry, that will depend on you.