This is going to be hard because as I write this, I've already read the 2nd book. And they're SO GOOD. But, they're different enough that the 1st book has its own flavor and energy. I also love the art and the humor and the little nods to contemporary life even if the story is about ancient greeks!
I guess I'd say the first book is the "set up" - here's the hero (Hercules), here's why he's doing all the stuff he's doing, here's his situation... and isn't he fun and cool and interesting? There's action, and monsters, and fights, and humor, and it's all fun.
Highly recommend! (but, plan on reading the 2nd book too)