This is the 1020th most frequent Swedish word.
fantastiskt
"Fantastiskt" means "fantastic" or "wonderful" in English.
Here, 'fantastiskt' is used as an adjective describing the positive and impressive nature of the act of learning Swedish quickly.
Det är fantastiskt att se hur snabbt du har lärt dig svenska.
It is fantastic to see how quickly you have learned Swedish.
In this sentence, 'fantastisk' as an adjective conveys admiration and wonder about the view.
Vilken fantastisk utsikt vi har från toppen av berget!
What a fantastic view we have from the top of the mountain!
Here, 'fantastiskt' emphasizes recognition and high quality of work done in the project.