Hmm. This is a tough one because much of the book is about the vagabond life, and so literally all the book could be interpreted positively or negatively about the topic.
That said, chapter 3 has a lot of pleasure in it, implying pros about the life. Chapter 4 is downright happy.
On the down side, chapter 5 shows how people don't understand, and how McCandless has to invent stories/lie to deal with this lack of understanding. Chapter 6 shows people trying to help/fix him. He specifically mentions "getting preached to death." Chapter 10 mentions someone like Alex who starved to death (pretty negative, no?), and in Chapter 11, money is very tight.
However, throughout those negative chapters, there are mentions of the adventure, and of the different dreams of how to live that make it hard to call them completely negative.