"Book 1: Rules", 64 pages, nothing new... but nice to have at the table as a reference document for the players.
"Book 2: The World of Glorantha", 64 pages, 21 pages about Glorantha in general (nothing new), 39 pages new about Jonstown
"Book 3: Soloquest", 60 pages, a Soloquest... but one that you as a GM, as well as each of your (new?) players can play multiple times
"Book 4: Adventures", 84 pages, two new adventures in and around Jonstown + a reinterpretation (second visit) to a well known classic
Map of Jonstown
Map of Northern Sartar
Maps of a cave complex
reference sheets
14 pregens (7 new and 7 old friends: fully fleshed out NPCs for you as GM!)
Just counting the four booklets and the 14 pregens:
300 pages total
ca. 200 pages useful also for veteran GMs.
2/3 of a Stater Set useful for veteran players is VERY good! Especially with this price tag.