Hands down the best graduate-level microeconomic theory book out there. The authors have a gift of explaining mathematical economics in an intuitive and reader-friendly way. I read the whole book at least 3 times during my MS and PhD, and it's always my to-go resource for any microeconomic concept. It is considered by many, and myself, the bible of microeconomics... and in many ways, it is! Even though the whole book should be required reading by any Econ grad student, the first 7 chapters are literally the best collection of the foundation of consumer theory. I can keep raving about this book, but you get the point. At this point, I should say that, coming into my MS I lacked a lot of math (A LOT). This book lies in this sweet spot of challenging you mathematically without being an overkill. Thus, even if, on first sight it might look tough to some, I would encourage you to take it on as your first Microeconomic theory book (it will likely remain as your last microeconomic theory book too - it's that good).
As if all this was not enough, there is a hidden gem in this book that many overlook. This gem is the book's Appendix chapters. If any incoming graduate student would ask me how he/she can best prepare for the PhD program, I would say go through the appendix of this book. It covers all the necessary mathematical concepts that a graduate student will need to go through not just this book but any first-year graduate course. It certainly even tops Krishna's "Auction Theory" book's Appendix (another great mathematical resource).
The only part which is not that amazing (still pretty good though) is game theory. For deeper insights into that area you should read Gibbons-"Game Theory for Applied Economists" (very introductory), Rubinstein-"A Course in Game Theory" (good level), Fudenberg & Tirole (advanced).