Those books are rather special for me. First of all because they represent a kind of book you don't find too often, so they are special as a rule. But there's a second reason, too: I doubt I can write something like this, although I've tried.
Those six books each contain three books that were originally sold separately. They were all more or less written by the same authors, namely Steve Jackson and Ian Livingstone. The six books on that photo were only sold once, they're not republished at the moment - as far as I know.
They are not meant to be read the normal way, meaning starting with the first page and reading until you've read the last one. Instead they are separated into about 400 small paragraphs, each of which tells a part of the story and at the end of each you can decide what to do next by choosing between two or more different options. For example:
"You have reached a cross-road. A street leads towards the east where you can see a mountain range. Another one leads to the west towards what seems a large city. The street towards the south seems to lead to a large forest full of old trees. Do you want to
go east read 215
go west read 350
continue south read 19"
After deciding on an option, the reader will continue with the paragraph belonging to the number mentioned. This way the whole story unfolds slowly with a lot of moving back and forth in the book. In addition - just like in a role-playing game - there are fights, there are things to be found and used. The books actually are some sort of one-person role-playing game that can be played everywhere: at home, at the beach, in the train or plane etc. I can even remember "Das Schwarze Auge" (a German role-playing system) publishing single-player campaigns working that way (I owned one, as far as I remember) for players to level-up a new character.
Of course, it's easy to cheat in such a game, you can read all possibilities before deciding, you can decide you've gotten all you need for the final fight, even if you haven't. I personally mostly assumed I was winning every fight, because I was more interested in the story than in figuring out the numbers for every fight in the books. And in the final battle it paid quite often to choose the decision with the highest number, because the "happy end" usually came with the last paragraph and number 400. (Although not always, I can remember there was at least one adventure for which this wasn't true.)
Most of the stories were fantasy - after all, Steve Jackson and Ian Livingstone are the founders of the "Game Workshop" and thus among the 'fathers' of role-playing everywhere. Nevertheless there's a few science-fiction inspired stories and at least one horror story. And there's more than one type of fantasy worlds, too (even though some adventures mention places from others).
I got one of the original books, "City of Thieves", when I was about twelve or thirteen, but soon after the books disappeared from the market for quite a while. Later on they resurfaced in a rather shabby paperback-version before being collected in those six large volumes (which together contain all the 18 books published by Jackson and Livingstone).
In a time before computer games became a prominent feature in the world, those books were a good way to play a role-playing game (or at least something of that type) alone. And even today they're a good way to spent some time, because they don't need any hardware (apart from a lamp, provided it's dark outside) to run.
Nevertheless, up until now I've never managed to write such a story myself, it's extremely hard to organize all the paragraphs.
But I'll go on trying!