Gibbon is a great writer, and this book is a monumental achievement,as was the empire it describes. But the time for both book and empire has come and gone.
Recent scholarship has cast doubt on many of the theories he espouses. And as for the prose, it is actually painful to the modern eye and ear. So I say give it a pass, read an abridged version, or get your Roman fix from other sources. There are plenty out there--ancient and modern concerning this fascinating historical era.