The complex, as mentioned already previously, should probably be an extension to the Istanbul WHS. It isn't even far from the main area of sites with a little touristy road full of shops leading you directly to the entrance. On first sight there is nothing special here. It is a relatively new mosque, 1755, built by the Osman family (thus NuruOSMANiye) with the typical minarets, signatures, ceiling prayers, mihrab, minbar and washing area outside. Whereas the mosque itself isn't special and you will feel that the Blue Mosque was ultimately better, there is more here although not all is accessible or still used for the same purpose. The sultan's pavilion can be seen from the outside, previously used to give the royalty a safe entrance to prayer in the sultan lodge. There are tombs outside of the mosque, a fancy fountain, and some other buildings (school, library) which are now closed or used otherwise. All of this is encircled in a large wall most people just use to cut through to get across. I cannot recommend seeking this out over all the other attractions Istanbul has to offer but if you attach it to your itinerary it should not take long to cover on your way. The metro and tram stations make it so easy to get around this lovely city.