In Locke and Key Volume 5: Clockworks, we get a ton of backstory. FINALLY! We learn where the keys came from, what's in the cave, what Dodge really wants, what the kids' dad did as a teen. This book was what i wanted much earlier! I get that this couldn't have been the first story but i feel like i would have liked 3 and 4 way more if i'd had some of this information earlier.
Just read online that there will be one more volume then the series will be complete. Excellent! I've found I'm growing to like complete stories more and more, whether they be books, movies or TV shows. Maybe because real life is so incomplete? So many things happen where you never find out the end of the story.
So hey, sometime next year there should be a complete series. YAY!