There are a few different types of Dragons, Blood dragons have a mean bite on Expert.
I am level 30 something and the hardest enemies are still dragons. Blood Dragons or Ice Dragons that is. Normal Dragons who haven't appeared for a long while and I might have seen 2 or 3 are not that strong. I call those 'baby dragons'.
Just as an FYI, Dragons are levelled. I'm level 35 and blood dragons are cake, but frost dragons still give a hard time.
dragon levels:
level 10 - Dragon
level 20 - blood dragon
level 30 - frost dragon
level 40 - elder dragon
level 50 - ancient dragon
level 20 - blood dragon
level 30 - frost dragon
level 40 - elder dragon
level 50 - ancient dragon