Absolutely. While modern many-body physics now includes topics like topological insulators and advanced tensor networks, the and diagrammatic expansions taught by Fetter and Walecka are the prerequisite "alphabet" for these advanced topics.
While various PDF versions circulate online for academic preview, owning a physical copy is often recommended due to the density of the equations and the frequent need to flip back to previous chapters for foundational proofs. If you are accessing a PDF for research: Absolutely
Modern "new" iterations of the course often come with updated problem sets or computational appendices provided by university professors (such as Stanford or MIT) to modernize the classic techniques. Is it Still Relevant in 2024? If you are accessing a PDF for research:
Step-by-step instructions on using diagrammatic techniques to solve many-body problems. Absolutely