After reading Pynchon's excellent, self-deprecating introduction to these stories, it is difficult to read the stories without searching for, and finding, elements of writerly clumsiness and naivete. The effect is similar to that of reading James Joyce's "Stephen Hero": the realization that even great writers were human in their youth.
I think of the preface to this book as the main body of the text, and the stories as figures and appendices elaborating on what Pynchon means when he criticizes his former self. I would not recommend this book for the intrinsic literary value of the stories -- they're not all that great, especially when compared with the Pynchon we more readily know. But as an essay about how not to write short stories, with some illustrations provided, or as a bit of Pynchon autobiography, Slow Learner is magnificent.