I will also bring up the first Spider-Man film. Take a look at the fight between the hero and Green Goblin at the end. It is a violent scene with a dark tone to it. It really feel like a fight to death, and the villain surely dies. And I can't spot anything "fun" during the fight, it's a very serious moment in the Spider-Man trilogy.
The makers of The Flash should find inspiration from it, and also from X-Men as I mentioned before.
Sure, the film can be entertaining here and there as the story plays out to us.... but I hope they don't give The Flash a too family friendly approach all the way. There needs to be a dramatic touch everytime the hero fights the villain. Just as Spider-Man, The Flash has to put an effort in defeating his nemesis, using all of his abilities to not get his *ss kicked. It should not be so easy that he can just fool around and mocking the silliness about the villain.
That is something we also want to see with Superman on the big screen. He should face somebody who actually can give him a fight worthy someone with his power level. That means no Lex Luthor (who only can use his brain to defeat Supes).
Now people finally understand what I mean when I say I want a more serious The Flash (I hope). I have given examples from both X-Men and Spider-Man, and people use to say Spidey is fun and entertaining. But the fun elements in Spider-Man trilogy aren't always loved by fans. Do I need to mention the "dance-on-the-pavement scene" with emo Peter Parker?
No it's the serious moments in that franchise that makes it good. Take away all the humour and the films will still be pretty good. Take away all the seriousness and only keep the fun. Then it would just be crap, even worse than Tim Story Fantastic Four.