Students first... There is a well-done website that accompanies the book, which includes outlines, sample tests & quizzes, and related study materials. The text is about average in terms of readability in comparison to other texts on the subject, and there are plenty of real-world examples to illustrate OM concepts (OM texts, as a general rule, don't read well). You may be able to get by with a previous edition if the textbook contents are your priority, but be advised, however, that the seventh edition contains some new and revised material, a few chapters have been re-arranged, and there are some different end-of-chapter exercises and cases.

For professors... You are probably already aware that OM can be challenging for the professor as well as the student, esp. with respect to where to aim the course - to the managers and generalists, or to the technicians & quantitatively-oriented. Heizer and Render have enough material to support either approach. The text is accompanied with ample instructor resources, including a CD and a website with slideshows, notes, outlines, and various other pedagogical tools. The testbank is easy to use, but should be supplemented with some quantitative short problems (if a quantitative approach is important to you).
Heizer and Render have also done a fair job of keeping the material up-to-date, which has resulted, after seven editions, in a pretty decent product. For me, the instructor resources and the comprehensiveness of the content (adequate support for either a managerial or quantitative approach) make Heizer and Render a good choice by comparison to other OM texts.