On a damp October day I visited the Manasija Monastery on the way back from a day out at Resava cave and Lisine waterfall which made for a very pleasant day of sightseeing.
The monastery was okay, as a building it was functional, nothing particularly impressive about it, a typical Byzantine style, orthodox church and monastic buildings and the fortifications were quite interesting but I did detect a certain amount of negativity towards me, as a tourist, from the priests inside the monastery and an Irish nun who ran the gift shop. I mean, if you don't want tourists don't have a gift and souvenir shop.
I love Serbia, it's one of my most visited countries but I have come across this negativity from the orthodox world several times there which is a shame.
Overall, the Manasija Monastery isn't somewhere I would say that makes a worthwhile destination, but combined with other attractions in the area (the waterfalls, caves, the eco town at Velika Plana, etc) it makes an interesting inclusion.
When compared to the fortified churches in Romania it doesn't quite hit the mark for me.