S'all good, except for this one thing...
The 'Green Rider' series is worth a read if you find yourself needing some light, easy fantasy. There's no arguing about that. Calling it medieval fantasy would be a mistake, as the society presented seems to be closer to a manner of 'Renaissance Age'—at least that's the best guess I can make when there is plumbing and museums with wax models—and it is hinted at that the Arcosians had machines. This, however, adds to the charm of the series.
In fact, many 'problems' in these books—the way Estoria's eyes suddenly and abruptly go from blue to green in between the first two books, the choppy writing in the first book, the occasional typo—are easily overlooked. The story is engaging, and Karigan is a protagonist who is easy to become invested in. The only problem with the series that I haven't been able to get over is the character Estoria.
If you ever needed an example of an 'Author's Darling'—a character who the author tries way too hard to make seem perfect and likable—it is Estoria. We are told she is clever and able to see through people, but we never see it. In fact, she is used by her cousin in the fourth book. That, however, pales in comparison to how she gets away without even a scolding for what is essentially date rape. In the fourth book, as King Zachary is dying and drugged up to the point of being only slightly conscious at best and confusing Estoria for Karigan (who we are made every aware doesn't have the same body type as Estoria, let alone the same coloring), Estoria agrees to a deathbed wedding (which was illegal, but she got away with that, too) and a romp in the sheets to make it official—even after being told she didn't have to do the latter. (Her angst over F'yran, her first love, is miraculously gone by this point.) No one is bothered by this, however, and Captain Mapstone even encourages Estoria to get closer to King Zachary.
With all the implied skills and talents, the loving descriptions, and the ability to get away with rape and breaking the law, Estoria went from a decent character to one that is hard not to hate. I can only hope that this was intentional, because otherwise it is an example of an Author's Darling in the worst way.