"Philosophical Investigations" is one of the most important philosophical books I've come across. As a recent graduate, I can testify that the time I spent studying Wittgenstein was some of the most interesting on my degree. Wittgenstein has a very common-sense approach in this book (unlike his earlier Tractatus Logico-Philosophicus, in which he attempted to make logical atomism answer everything) and the majority of the book consists of breaking down philosophical problems and exposing them as not really being problems at all. In a sense, Wittgenstein's philosophy is the erasure of philosophy and a caution to other philosophers.
In the foreword, Wittgenstein writes that he would "hate for his writing to save people the trouble of thinking" and he certainly acheived his wish. Many people find Wittgenstein very difficult to understand even when they've been studying philosophy for years, so this is definitely NOT a book for someone who is unfamiliar or unconfident in reading philosophical texts.
Nevertheless, for someone interested in philosophy, I think this book is a must. And this particular edition is well worth owning. The translation is excellent - it feels easy and natural and full of personality. Plus, the original German is printed opposite each translated page. This is particularly helpful for a student wishing to fully engage in the text and deconstruct the work, since naturally some terms in English may be ambiguous, whereas in the original German the meaning is clear (take the two senses of "meaning", for example - "meinen" and "Bedeutung").
So if you love philosophy or consider yourself a philosopher, I would recommend you this text, especially in this edition. If not, steer clear. You won't get much out of it except frustration.