This novel tells how the events in the beginning of the Eye of the World came to be. How Moiraine (and Lan) started the quest for the Dragon Reborn, and why she knew it must be a kid from the Two Rivers. It also shows some great scenes which are reminisced about in the main books, like (tFoH) Moiraine talking about finding a pond to teach Lan humility or the test to the shawl and generally more about Accepted life, or the Foretelling of the Dragon's birth, the Aiel War/Bloodsnow, etc, etc... We encounter some of the important Aes Sedai in the main series (Verin, Elaida, Cadsuane, ...) with new insights on their personalities and personal history.
For me, it was a relief to read New Spring after books like 8-10, because New Spring is fast, things unfold really quickly, the storyline is simple, it doesn't jump in dozens of POVs, etc... I love the deepness of the main series, but coming into Crossroads of Twilight, it had nearly come to a halt, like 1000 pages telling about 2 weeks, no progress on many plots, etc...
The bad news is, nobody knows yet if the missing 2 books will be written, far less by who, and when...