This is the 557th most frequent German word.
ziemlich
Quite; fairly; rather.
In this context, 'ziemlich' is used as an adverb to indicate 'quite', suggesting a noticeable but not excessive degree.
Das Haus ist ziemlich groß.
The house is quite large.
Here, 'ziemlich' modifies the adjective 'überrascht', implying a significant level of surprise.
Er war ziemlich überrascht von den Neuigkeiten.
He was quite surprised by the news.
In this sentence, 'ziemlich' is used to soften the intensity of the adjective 'schwierig', indicating a non-extreme difficulty.