I find the spiritual pursit and continous " Tazkeya " practiced by the sufis something that should be expected from every muslim..and i am disturbed when people think it's only restricted on sufis
However , many sufis go with their spiritual pursuit to the extreme ignoring the essence of islam which is moderation and its dual nature that combines both the spiritual and the material or the mundane
The other thing ,is that many of them borrow concepts from the non muslim mystics which is extremely dangerous to a muslim's creed to the degree that could possibly bring them entirely outside the boundaries of islam
honestly ,i read some sufi texts for the purpose of tazkeya...but with extreme cautious...because perserving one's pure islamic creed comes before tazkeya or whatsoever
n.b .Tazkeya : cleansing of hearts ,actions and morals -ehancement of virtues and excelling of moral values ( it's an entire huge subject in islam )