There are many stunningly beautiful paintings to be found in the Campania, but it's important to remember that neither Pompeii nor Herculaneum were Rome.
There must have been magnificent pieces in the city and when I want to see one such example I always return to the same painting, one from Livia's villa at Prima Porta.
This is one part of a much larger painting (late 1st century Bc). You find other scenes that have been posted earlier here and here. You may also want to compare it to this painting from the villa at Oplontis (which may have belonged to Poppaea, Nero's wife. The evidence is not very convincing though)