In my experience, the quality is quite awful. Stitiching is quite messy on a lot of basic lines eg loose threads/missed stitches and Zara t-shirts wash badly, losing their shape at lower wash temperatures.
I don't know where they purchase their low quality cotton from but its on par with H&M in terms of fabric quality and construction; you just pay more for the better design.
I pretty much agree with this. The price/quality ratio leaves much to be desired. I wouldn't buy anything from there again.