"Han Solo at Star's End" and its sequels ("Han Solo's Revenge" and "Han Solo and the Lost Legacy") blew my little kiddie mind.
First released in 1979, they were windows into full adventures just like the ones that I'd had with toys, but fully fleshed out, and introducing a full cast of characters beyond the ones I'd grown to love through the films.
The trilogy covers Han & Chewie's adventures before the films began. It'll probably come as no surprise that they're depicted as smugglers with hearts of gold. They may complain along the way, but when push comes to shove, they always set aside their own interests to help out those less fortunate than them.
I can't objectively say how well these books are written, as I haven't revisited since childhood. But I can say this: as a kid, they were friggin' magical. I read and re-read them, bringing them along on family vacations and into all my favorite secret reading spots tucked away in the backyard, where I felt I was in a world of my own.