Well they dont really have a similar type of engine, one is open world with non-zoning interconnected areas, the other was heavily instanced with zoning and only a few people in most places at once. They were similar in regards to them both being fantasy based with spells and monsters, but in terms of what each engine did and was constructed to achieve they werent that similar. If GW1 is similar to WoW then you could claim that Neverwinter Nights was similar. The fact is that GW1 was designed in a way that didnt involve the same requirements as an open world MMO, so I wouldnt feel comfortable comparing the two of them directly. Now GW2 is open world and I would feel perfectly comfortable comparing that to another MMO.
i meant the graphics engines were similar and most mmos have zones, guild wars could easily have been an mmo with zones that werent instanced to one persons group its how mmos mainly are anyway , wow is fairly unique in the way interconnected areas on the same island arent seperated by loading screens but that has little do do with the graphics beeing how they are