I used to really struggle with finding the meaning of the series vs. the individual book. Does it have both? And while there is usually this grand kind of meaning the story has, I found that each book really works best when it has its own unique controlling idea and if a "series" has a bigger idea, that's usually found as the controlling idea of the last book in that series. That's when you really deliver the series/season "meaning". A lot of these controlling ideas have gradients. So an entire series can be about "love vs. other values" and each book/episode makes that controlling idea tangible in a very specific/unique by exploring a different facet of that same idea.