This is a novel mostly written by Robert Parker, drawing on four chapters started by Raymond Chandler at the end of his life. If you are looking for a great Marlowe story done just like the early ones, you will be disappointed. If you are glad to have one more chance to be with Marlowe, I think you will be pleased with the experience.
The story is a natural for Parker, because it involves Marlowe marrying a rich society woman on the spur of the moment. Having gotten together, they both realize that not all is right in this relationship. 'Can't live with him, can't live without him' could have been the title. The relationship raises a lot of the kinds of issues that Parker handles well in the Spenser stories between Spenser and Susan.
Marlowe keeps at his detective work, and we meet a whole cast of hard characters portrayed with wonderfully terse dialogue and understatement. Although not as tough as a Chandler, it is certainly tough in an appealing Parkerish way.
Having grown up in Southern California in the 1950s, I could relate to the tale that Chandler/Parker have woven. It seemed to fit my memory of those times, and had a sort of smoky, boozy nostalgia attached to it.
Give it a try. The first five chapters are only about 26 pages. You'll have a good sense whether or not you want to read more. I know I could not have possibly put it down at that point. I was hooked. Maybe you will be, too. I hope it will be irresistible for you as well.