Caveat- my kids loved this and immediately demanded to read more in the series.
But seriously- this book was really silly. Sometimes it was silly in a fun way (the intro is hilarious, the beanstalk is a very silly touch). But sometimes just badly written. The characters have absolutely no discernible personalities. If you squint really hard, you can see them trying to line up against the archetypes of a bad 80s movie- Hades is the joker, Poseidon is the jock, Demeter as the sensitive one, Zeus as the leader. But they regularly forget what personality they were supposed to have and just deliver lines to keep the plot moving. The plot moves at an absolutely frenetic pace, whether or not it makes sense. Things need to happen just to keep the action moving. I think this is why my kids liked it so much- there was constant peril. But the peril gets monotonous after a while.
It's not actively terrible- it's not that it has a bad message, it just has no message. If you are a Greek mythology superfan, you might enjoy this. If you see your kid excited about this series, smile and suffer through it. But don't expect much.