Percy is a natural-born storyteller. His goal is to tell his story and to tell it well. He wants us readers to be able to understand and imagine everything exactly as he sees it. As a result, he gives us lots of detail, describing the setting everywhere he goes. We get a high-def, front-row-seats experience of his quest. Check out this description:
My shield was the size of an NBA backboard, with a big caduceus in the middle. It weighed about a million pounds. I could have snowboarded on it fine, but I hoped nobody expected me to seriously run fast. (8.103)
Can't you visualize the shield? Can't you almost feel how heavy it is in your arms? Can you see the "big caduceus" decorating its front? This is the power of Percy's storytelling: we are able to be right there with him.
He also knows when to be brief in his storytelling, giving us just the facts. Let's face it, Percy's got a lot of ground to cover in telling this story, so it's helpful when he cuts to the chase. Check out this moment:
Confession time: I ditched Grover as soon as we got to the bus terminal. (3.1)
In this tiny sentence, we are able to visualize Percy ditching Grover at the bus station, and we also understand that he feels a bit guilty about this (why else would he call it a "confession"). Percy (or Rick Riordan) is a master at knowing when to fill us in on all the juicy details and when to keep the story flowing and moving along.