"Playback" sure is a rather disappointing last Marlowe novel in that it doesn't pack most of the excitement of its predecessors. It's not set in LA but Esmeralda, and this time Chandler's characters all feel a little too cliché. As a fellow reviewer remarked, it feels like Chandler was just going through the motions.
Nonetheless, "Playback" has a few things going for it - first and foremost, it still is Chandler and Marlowe. Marlowe is still the same character the reader of Chandler has come to love, even though I felt that his memories of and feelings for Linda felt a little out of place. But maybe that's just Marlowe getting old and lonesome; it fits the character if you think about it. Also, it's a pretty short read, so you'd only lose one or two evenings in the company of your trusted PI - I've had evenings far worse than that.
If you love Chandler, don't hesitate and buy this book, if just for the sake of completeness. It's not as good as the rest of the Marlowe mysteries, but it still is Chandler. And by that, it still is better than most.