The Millions (what the heck is this website? I don’t even know) posted an interesting list of series’ you may have missed as a kid but should try as an adult. Since I personally have two of those series’ on my to-read list I thought it was probably a good list. So I’m sharing.
1. The Wolves Chronicles by Joan Aiken
2. Howl’s Moving Castle and Castle in the Air by Diana Wynne Jones (on my to-read)
3. The Stanley Family series by Zilpha Keatley Snyder
4. The Half Magic Series by Edward Eager (also on my to-read list)
5. The Vesper Holly series by Lloyd Alexander
Check out the descriptions through the above hyperlink.