Heidegger has been the biggest gap in my reading. He is the one major figure in philosophy that I haven't read -- and hence, everything that flows from him (mainly 2/3rds of modernity) has also been a blank book to me. So for someone looking for a way into this -- this book is just excellent.
On the other hand, Harman tries to cover too much to briefly -- and so I found my eyes glazing at some of the ancillary issues, which were simply not well-enough prepared.
On the other hand -- I'm started to sound like a two-handed economist here -- Heidegger is one of those thinkers (like Plato and Einstein) who thought he had only one idea -- albeit one BIG idea -- and here Harmen does an excellent job.
That one idea, of course, is Dasein -- or more particularly the notion that Dasein is an event.
Could place to start, and my thanks to Chris for calling this to my attention.