Many tourists choose to use Medan as a quick thru-point to travel elsewhere in Sumatra, but the city offers a glimpse of a large Indonesian city still unfrequented by western tourists, and shouldn't be quickly dismissed. However, Medan is more chaotic and has a bit more litter than Jakarta or Denpasar and open sewers abound. Furthermore, not as many people speak English in Medan as in other large Indonesian cities, but even a short list of useful expressions goes a long way, and Sumaterans are still unjaded by westerners.
Medan hosts a great lot of very nice Art Déco buildings from the Dutch colonial era, like the Old City Hall, the Post office, the Great Mosque and many business buildings in and around Jl. Ahmad Yani. Some of them are in horrible shape, but most of them maintain their old splendour.