> Nephew feels more like Lewis' earlier science fiction novels, while Wardrobe has a fairy-tale quality
Will vouch for this. I started Narnia in my early teens. I knew Wardrobe to be a classic but the edition the bookstore carried had Nephew labeled as the first book. Honestly? I felt kinda short-changed at what I got. Nephew set-up this expectation of being a myth-heavy story, something in between Harry Potter and LOTR/Earthsea in terms of world-building. Jackson's LOTR was at peak popularity at the time too so I really lapped Nephew up.
Honestly though, I loved every book in the series. I can understand why people might have issues with Caspian---maybe the weakest book in the whole Chronicle IMO---and looking back now the Christian imagery might be heavy-handed at times. But as children's/early teens' fantasy series, the stories and the world are entertaining. Which, as a teenager, was all I really needed of the books. Maybe Lewis' only fault is that he peaked too early with Wardrobe, setting up expectations for the rest of the series.