Rapsani is quite a lot warmer than Naoussa, also Naoussa is 100% Xinomavro and Rapsani uses Krassato and Stavroto in support. You could draw parallels with the difference between a Northern and Southern Rhone in style, in that Rapsani is broader and more generous.
Naoussa is probably my favourite Greek appellation and the Thymiopoulos wines are made in a relatively modern and accessible style, without losing typicity. Some more old fashioned Naoussa are pretty much tannic monsters (not that I mind this).
Really good wines and I think great value when compared to Burgundy or Barolo for example.