What is the best series of books you've read? and why?

A few years back I read the Deptford Trilogy by Robertson Davies, if you haven't read these 3 books you should (Fifth Business is the first). There is lots of Jungian psychology in them. Davies was an exceptional writer.

http://en.wikipedia.org/wiki/The_Deptford_Trilogy

Good pick. Personally I'm a big fan of Salvatore's Drizzt series, which is going on about 20 books by now. It's set in the Forgotten Realms D&D setting, which is more or less classic Tolkienesque fantasy. Unlike many other D&D novels it has very well developed and likable characters.

I liked Lord of the Rings immensely, but I'd have to say the best series was The Chronicles of Narnia. I've read the series seven times, and Voyage of the Dawn Treader I've read about 10 times.

The Chronicles of Narnia. Although, written for kids, I could relate it to it on a spiritual level, added to that very enjoyable.

I also liked the Lord of the Rings. Agree with Simey's comments.

I don't know if you would call it a series but I HAVE read every book by John Irving.

I have also read every Star Trek book written by Peter David.

Why?

I obviously enjoy those authors.

I read the first couple hundred books in The Executioner series, too back when Don Pendleton was still writing them. They were the best in terms of being the first to have a one man war against the mafia storyline and inspired the Punisher comic books in fact. Pendleton seemed to be quite an expert on all the weapons used in the series almost to the point where ti almost slowed down the story.

If you are into Tolkien then you need to read a book called BORED OF THE RINGS. It's The national Lampoon take off of the series and it is hilarious. Also Peter David writes a series with a character called SIr Apropos of Nothing. That is funny and sometimes reminiscent of Tolkien as well.