For me this was the most exceptional Monastery in Portugal. The whole structure is photogenic, well-kept, and simply a lovely place to explore. The weather during my visit was perfect, it really does make a difference when visiting world heritage sites. 

The royal tombs here are all finely detailed. The Cloister of King Afonso is undeniably beautiful and with a blue nearly cloudless sky, it was very pleasant. Truly, a historic site that I will miss walking from within, wonder to wonder, and then arriving to the unfinished chapel and finding myself smiling. The detail in the later open-air chapel was astounding and a bit absurd! My visit took around an hour, but by the end, returning to the car, my wife and I were just full of enjoyment of the drive, the history, the gorgeous weather. No complaints.

Much has been stated here about "Manueline" or Portuguese late Gothic style architecture. While it surely is over-the-top, this description cannot even begin to be imagined when you compare how over-the-top every building in Sintra is, no? Can something over-the-top still be admired and charming? Surely, yes. Sintra, despite its vanity, is a lovely place to explore. So I don't really understand this critique, but this monastery which just passed its 500 year anniversary is certainly a religion gem worth visiting and seeing for oneself.