This book is pure genius in the most literal sense, and is without a doubt the most important philosophical work to be produced in recent years (and possibly ever). Whilst Heidegger is suitably well read (and taught) in the academic world, the full implications of his insights have yet to 'sink in' fully. Once this has happened Heidegger's thought will most certainly be seen to be the foundation of a truly momentous paradigm shift in consciousness and thought on a general level.
It is frequently asserted that Heidegger (and in particular Being and Time) is almost completely impossible to understand. This may well be true for those readers that attempt to 'dip in' to his works; or who wish to read something at speed. There are no 'quick insights' to be gained from Heidegger. However, anyone with a modicum of patience and the ability to study rather than simply read will not have this issue. A small amount of preparatory reading (especially of Husserl) also doesn't hurt.
The main difficulty is the language used, however this is simply something that one gets used to by progressing through the book. The introduction may seem impenetrable on first reading; but read it again mid-way and afterwards and it makes complete sense.
A note on the translations: this version (Macquarrie and Robinson) is by far the easiest to read, and is the closest to the original German. The alternative (Joan Stambaugh), whilst it has been designed to be more accessible, is actually somehow a lot more confusing. However, be warned: the Macquarrie and Robinson version leaves all Greek terms and most Latin terms completely un-translated, which can be very irritating. It may therefore be advisable to have both copies.