This is absolutely not the place to start reading Lovecraft and is only for Lovecraft aficionados. Half the space of the collection is given over to two novellas: The Dreamquest of Unknown Kadath and the Case of Charles Dexter Ward. The Dreamquest is a grand tour through the Lovecraftian mythos and points back and ahead to all sorts of stories. It is not exactly good though and is told far too fast to work. It's amongst the weakest of Lovecraft's stories, but is fascinating to anyone who is familiar with his work. Charles Dexter Ward is much better and works very well and is a fairly typical Lovecraftian tale. In general the other works have a tendency to get better as they go along, but virtually nothing is without some interest. The Dreams in the Witchhouse is one of Lovecraft's best tales and it is surprising that it did not make it into The Best of Lovecraft anthology which is a companion to this collection.
For the Lovecraft fan only. Do not start here, but read and enjoy if you like him a lot.