For the second sentence, "the end" is translated into Korean as "끝" or "마지막" but, the translated sentence in above answer "끝내는 것 같아요." sounds a bit weird. I suggest that you can say it as
- I think this is the end = (I think 제 생각엔) 이것이 마지막(or 끝)인 것 같아요.
Also, for the last one, it is better to translate it as below
I think this book is very interesting = (I think 제 생각엔) 이 책은 아주 흥미로워요.