The flu attacks the upper respiratory system (nose and throat) and we have a vaccine for it. The Novel Coronavirus attacks the lower respiratory system (lungs) with viral pneumonia. That makes it about 10 times more deadly - but there are still too many unknowns to know how bad it will get.
There are also indications it causes violent convulsions and death. Whether that is because it attacks the brain, or when people can no longer breathe they go into convulsions, I don’t think anyone knows