[It's past midnight, so all that's a bit rambly. Her website should help clarify anything odd I phrased below this].

There's also a collection of short stories simply titled Tortall and Other Lands which I recommend, though one of the stories is set after the Trickster Books, so read those first.

The Circle books are well written. There are two quartets I believe, and one stand alone novel (plus one made-for-audio drama that was later transcribed as a book) - more to be written (along with some new books about Numair).

Within the first quartet there are 4 main characters, mages, and their lives are shown as they grow up and learn their craft (each book is 'about' one character, but all 4 appear)- comparable to how in the Tortall books they had knight training. In the second quartet each book focuses even closer on the individual mages, and continues with their stories as they grow up.

I believe Pierce has said the books are more inspired by the East than Tortall's European outlook as well- you see more diversity than from what I remember being shown in Tortall, and the magic system is different than The Gift- discussed far more in depth. Personally I also think that the setting is a bit more 'in the future' than the straight-medieval of Tortall, but not by very much. The difference between oh... the 1300s and the 1600s, perhaps?

So yes, certainly read them. Highly recommended.

Also with the Tortall books there should be another set you missed- There's:

Alanna's story (Song of the Lioness),

Daine's story (The Immortals),

Kel's story (Protector of the Small),

Aly's story (Trickster), and

Beka's story (Provost's Dog)- Beka being an ancestor of Alanna, but the latest series that just finished last year.

So that's 17 books in Tortall, and the short story collection.

Circle has 10 books (two quartets, two stand alone books).