Poor built quality, low quality materials, problems with replacement of items under warranty, no response or delays when you want to report an issue etc.
Good friends of mine live in DAMAC building in Business Bay and they have constant issues (fire alarms go on daily and in the night, gas leakages, problems with hot/cold water, kitchen appliances broke in warranty, etc). I even met the architect of that building and he told me that damac have changed materials with cheaper ones during the construction︀ (replaced marble with tiles etc).
I know damac also has luxury projects so these are︁ probably of better quality (damac cavali tower or damac hills might be a better quality)︂
Emaar is probably a bit better (no personal experience though).
If you have the money︃ then you should check out Select Group or Meraas. Or even some smaller boutique developers︄ if you're looking for something specific.