Series Vs. Stand Alone

Lyda brings this up below and now that I've got some time I wanted to take a slightly longer look at it. As with so many things in writing I don't know that I agree that this is an either or question, or one that can even hope to come up with a real answer. The reason I suggest this is that readers and writers are neither monolithic in their opinions as groups or even as individuals. I know that I have different answers for this as a reader, as a writer, and depending on who we're talking about reading.

As a writer I love world building most of all, an activity that is definitely curtailed by multiple books in the same world. You would think that would put me firmly in the stand-alone camp, but it doesn't. I have trilogy and tetralogy proposals both out making the rounds attached to the first book of each and I have high hopes of getting to write the rest in each series. Now, you could argue that those are each multi-part books a la Lord of the Rings, and there'd be some truth to that. But each book also has it's own (hopefully complete) story arc that should allow someone to read it individually with satisfaction. Beyond that I've got the WebMage series which is an open ended set of books each with its own arc but each tied to events in the other books, and I'm having a grand old time writing it, in part because it's teaching me things about character and how to make that grow and evolve while staying true to a core. On the other hand, 7 of the first 8 novels I wrote were stand-alones that I wrote with no intention of ever writing a sequel. On the other other hand, one of those is WebMage.

As a reader the answer is even more complex with me loving some writer because they don't repeat and others because they do, and not even being consistent about why I love either type of writer. I love some series because of world and am delighted that writer jumps around to different sets of characters exploring this grand place the writer has built. I also have stopped series after the second book, because what I loved about the first was the characters, and jumping around to different sets of characters to explore the world bores me to tears.

So how about this for a question? Are there series that you love? If so, what do you love about them? The people? The world? The plotting? Something else entirely? Is there any constant from series to series?