Each chapter is standalone. Thus if you want to see all the content, you have to download all chapters and play each chapter.
Usually separate chapters get created due to either engine demand (too many pictures in archives impact on loading times), or alternatively, because content in earlier chapters does not change, it could lead to people downloading and redownloading the earlier content over and over again. And for people with limited bandwidth, that is really not great.
In this case, Chapter 1 and Chapter 2 are done, while Chapter 3 is still getting updates. So I would suggest to download chapter one, and if you like it, go for Chapter 2 (and later Chapter 3, but that might be finished by the time you are done with Chapter 2).