Is it book or novel?
I saw in google it has some pages full of sentences only and the other are pictures.
Are the pictures pages as same amount as sentences pages?
Where to buy it?
If you want to simply want to read lots of words you might be better checking out the newer RuneScape novels: Gift of Guthix & Fall of Hallowvale.
But, the 20 Years is a fascinating book, lots of very cool behind-the-scenes information from various different J-Mods, some of which I was unaware of until I read it myself!