Sergei Lukyanenko's "Night Watch" books were always billed as a trilogy and when a fourth arrived they were a bit too dark to go for the Hitch-Hiker's Guide tongue-in-cheek route of continuing to call it that; so The Last Watch is billed as a sequel to the entire trilogy. Maybe the publishers should just get round to calling it a series as at the end of the book Lukyanenko drops a pretty heavy hint that the word "Last" in the title shouldn't be taken too literally.
For the most part this follows the format of the earlier books, being made up of two novellas whose stories then come together in the third. The biggest change is to location, as Anton (now a Higher magician, pretty much by accident so not entirely in control of his new powers) has to leave the familiar territory of Russia. First to Edinburgh, where he has to represent the Moscow Night Watch when a Russian tourist is murdered by a vampire there; and then to help a usually quiet Watch office in Uzbekistan when the search for a long-lost magician gets out of hand. All this is linked by a plot to get hold of artifacts created by Merlin himself; something that holds some personal significance for Anton as the only Other in history to have as much power as Merlin is his own daughter, still a toddler.
If you liked the earlier books this is definitely worth adding to the collection, the series retains its po-faced intensity and Lukyanenko continues to make his fantasy world seem fresh and properly fleshed-out, while adding a few changes of scenery into the mix as well.