check it out here.
Most of the strips from the first two volumes have never been reprinted, and includes the first and only time that adults were ever seen in the strip (those strips are in volume two).
No new characters are introduced in Volume 3, but we do see the last of a very little seen character, the loud mouth Charlotte Braun. (who looked just like Charlie Brown but without the jagged sweater and with curly hair).
What I find so great about these 50 year old strips are how brutally honest the characters are. Check out these first tier panels from an early 1955 Sunday strip:
Hopefully Fantagraphics will fulfill this commitment and complete the entire Peanuts run. In the past they've begun other comic strip reprint collections but haven't finished them. In any event, if you're a Peanuts fan or are just looking for some good summer reading you can't go wrong with The Complete Peanuts.