These four "Meditations" deal with, as has been noted in other reviews, a very diverse number of topics. Primarily, however (and apart from the scattered passages of philosophical interest), they are criticisms, or more accurately explanations, of culture. Although they deal with issues such as sholarship, literature, science, art, and of course philosophy, the recurring theme in all four is culture. What it is, what kind of culture is desirable, how culture comes about, etc. These discussions are found in each of the Meditations, some more fragmentary than in others.
These are some of Nietzsche's early writings and they reflect that fact. They are similar to "The Birth of Tragedy" to certain degrees in style and in content. They are not fully or even primarily philosophical works. Nietzsche is here still under the influence of Richard Wagner and Arthur Schopenhauer and although it can be seen that he is breaking away from those influences (for instance, the Meditation on Schopenhauer does not focus on Schopenhauer's actual philosophy as a source of education for Nietzsche so much as Schopenhauer the man, and the Meditation on Richard Wagner is not as strong and unified as the other Meditations are and it does not present a wholly flattering picture of Wagner, dwelling as it does on his psychology - it's tenor is not always one entirely of approval) he has not really begun his philosophizing yet.
The other way they show how early on in Nietzsche's career they are is in the writing itself. While "The Birth of Tragedy" had technical issues even ignoring the philological and philosophical concerns (as amazing a work in aesthetics and culture as it was), these four works do as well. Don't get me wrong, even in Nietzsche's first book his command of language shows itself and these are beautifully written pieces in their own right, but neither his first book nor the four Meditations can quite measure up, stylistically, to Nietzsche's later works like "Twilight of the Idols".
Still, the Meditations are interesting in their own right. "David Straus, the Confessor and the Writer" deals with a number of topics. One of these has to do with faith and doctrines of beliefs. Nietzsche, who used to enjoy reading Strauss's "Life of Jesus", blasts Strauss mercilessly (in a way that really hasn't changed if you happen to watch any TV at all) for putting up his own secular faith in place of religious faith and you can almost hear the unspoken words "Last Man" which Nietzsche would write so contemptuously of in "Thus Spoke Zarathustra". The fact that Strauss shared similar views on religion as such with Nietzsche mattered little. Strauss, in Nietzsche's opinion, tried to change the fundamental views of the world (from the supernatural to the material/deterministic) without drawing new conclusions from that. Basically, Strauss was viewed as one of those who saw Darwin and that which he stood for as of great benefit to mankind without realizing the kinds of change such a shift in worldview that implied. Essentially, Strauss represents the type (the Last Man) that has ultimately been victorious, in large parts of the world, over Nietzsche. The kind who shifts his superstitions to material science but keeps the Christian morality, or the Christian conclusions based on that premise (which, because of the shift from afterworld to this world, is no longer a valid premise).
Later on, Nietzsche bashes Strauss's prose, although the final examples of bad German that Nietzsche picked apart in the original are simply cut out of this version because of the translation difficulties. It would be somewhat pointless to hear a German criticism in German _of_ German if it has all been rendered (deliberately badly) into English.
"On the Uses and Disadvantages of History for Life" is an interesting piece which points out a central tenet of Nietzsche's philosophy of life. A thing may only be "good" to the extent that it is life-promoting. This is, I'm pretty sure, the main reason Nietzsche fought so hard against anything he perceived as nihilistic. Nietzsche says in here that to a certain extent, for man to function, he must be "unhistorical". On the other hand, he applauds the type who can be as historical as possible and still function. Throughout these meditations you get a sense of Nietzsche's approval of the "higher" or aristocratic type that was to culminate in his conception of the overman.
"Schopenhauer as Educator" is, as I have said, not so much about Schopenhauer's philosophy as it is about the lesson's Nietzsche took from Schopenhauer's life. Nietzsche claimed, towards the end of his life, that this essay was not written about Schopenhauer but about himself. While I don't really buy that, I am inclined to grant, after reading it, that some of the attributes Nietzsche praises in Schopenhauer were either slightly altered or completely fabricated and that Nietzsche was writing into this Meditation things he admired and wished to emulate. For one thing, I don't think you could really say that Schopenhauer was "cheerful" in any sense of the word. Schopenhauer was a pessimist in more than just a philosophical sense and his writings about anything contemporary or tangible seem bitter (not just the stuff about Hegel).
I'll leave off the final Meditation. It's not as clear as the others, but there is a lot of interesting cultural commentary, including a very great deal about art and culture. There is one passage I would like to quote as an example: "Wherever 'form' is nowadays demanded, in society and in conversation, in literary expression, in traffic between states, what is involuntarily understood by it is a pleasing appearance, the antithesis of the true concept of form as shape necessitated by content, which has nothing to do with 'pleasing' or 'displeasing' preciesly because it is necessary and not arbitrary." (Richard Wagner in Bayreuth pg. 216)
Although there was a revolt against form in the early part of the 20th Century, like most revolts it made certain gains and was summarily crushed.
These Meditations constitute necessary reading for any serious Nietzschean (and I use that term without any sense of irony - if Nietzsche hadn't wanted adherents he shouldn't have left any writings, unsystematic or not) and help greatly with a proper understanding of his ideas (which can be misconstrued if you start with later writings and don't read them analytically).
This translation is, of course, excellent and the Cambridge Texts series is about the best on the market right now. Even though I have the paperback editions of Nietzsche's works the binding is more durable than some hardcover books I have purchased.