I've never read a Shazam comic. Most of my knowledge of most comic book characters comes from those that had either animated or live action TV shows. I only mention that to highlight that I had no real expectations of what this movie might be.
The trailers suggested that Shazam was very much a comedy. That made it more interesting to me given the more serious tone of previous DC films.
What surprised me is, while it is very much is a comedy, it still fits in well with the tone and style of any of the DC films from Man of Steel (2013) onward. (Although it's never going to happen I think Zachary Levi's Shazam teamed up with Ben Affleck's Batman would make for an amazing movie).
Anyway, I digress. Shazam is the story of an orphan boy who is given the powers, and can transform into an actual superhero. As you would expect, your average, nearly fifteen year old boy, isn't necessarily ready for all that power, and it's not too long before he discovers he has an arch nemesis, hell bent on taking those powers away.
The film is cast really well with all the kids looking like actual kids rather than adults playing kids. Asher Angel is innocent and believable enough as Billy Batson to be a worthy successor to the mantle of Shazam. However the movie really picks up when Zachary Levi makes his appearance as Shazam (though he is never called this during the entire film).
Zachary really captures the sense that, although he's clearly a fully grown man, on the inside he is still 14 year old Billy Batson. Even better is the relationship between Zachary and Jack Dylan Grazer, who plays Billy's only friend, and foster brother Freddy Freeman. The two of them together, as they explore Billy's newly found powers, makes for some fun dialogue and situations.
Mark Strong, as the villain, Dr Sivana, doesn't have the strongest of motivations for a supervillain but his performance is suitably menacing, providing great contrast to the silliness of Billy's initial reactions to being a superhero. Even though this movie does have a lot of CGI it was nice to see the main bad guy was kind of scary just through his determination to get what he was after at any cost.
Throughout the movie there are a lot of nods and references to other films (not that I could begin to name them all), often to poke fun at superhero film tropes. I particularly liked Dr Sivana's villain monologue part way through the final battle (not really a spoiler because it's the joke of that situation that makes it memorable - and all villain's tend to have an expository, this is my plan, scene in superhero films).
Overall Shazam is a fun movie. It's almost the Superman film you wish we had over what we actually got, because Zachary plays Shazam very much along the lines of the way Christopher Reeve played Superman - if Superman was possessed by a 14 year old boy maybe?
Billy Batson maybe a bit of an angsty, cynical teen, but he sure enjoys being a superhero, and has fun with it. Subsequently that makes this film a lot of fun.
It's more of a family film than DC's previous outings but it's still edgy enough that maybe you might want to see it first before showing it to your younger family members.
As far as superhero films go, it's not stand out amazing, but it is a film you may go back to just because you remember it was fun. I'd definitely go see a sequel, and I'd really like to see Shazam team up with any of DC's other live action heroes - because I think that could present a really interesting dynamic.