This is the standard graduate-level intro to QFT text; at least it was in 2000s when I was in school. It's got the same clinical, serious, joyless air as other "canonical" graduate texts like Jackson; it's rigorous but long-winded in places, making it a formidable opponent to anyone seeing this stuff for the first time. There is a strong focus on QFT as a calculational tool, and if you ever plan on computing multi-loop corrections to scattering amplitudes, this book is probably the only show in town. The coverage of path integral quantization and renormalization group theory are also some of the best I've seen.
But, unless you seriously need to kick the shit out of quantum field theory, there are more relaxed, conceptually-oriented, and well-written texts out there, like Mandl & Shaw or Ryder.