I purchased this for my first year econometrics class. It covers the necessary content, and the mathematics is appropriate for econ grad students. However, I find it to be poorly formatted. I would prefer a more didactic presentation of proofs, but here a lot of important expressions and equations are tucked away in the text, rather than given their own line. In general, I find the presented proofs and lines of reason to be somewhat difficult to follow.
Another big problem is its use of examples. Throughout the book, the authors make ample use of examples to illustrate concepts. The further you read, however, the more the authors make references to previous examples rather than repeating the information they feel is vital to understand the current example. Moreover, examples refer to examples refer to examples, etc.. This might be useful when you read the book through for class, but it will make it a terrible reference tool later on. I am currently considering a different text, such as Hayashi or Greene. Consider purchasing a more mainstream and well-considered econometrics text for your bookshelf, and go in with your classmates to purchase a single copy of Heij if you need to do problem sets out of it for class.