Nothing wrong with it. The only problem is that we tend to abuse this expression and, consequently, we sometimes hear people using I think... six, eight, ten times in a very short period of time like the oral exam.
One of the factors that influences the final marks in the oral exam is the variety of structures and richness of vocabulary students use. So why don't you try and learn these other phrases to introduce your opinions?
In my opinion ...
In my view ...
Personally, I think ...
Personally speaking ...
It seems to me that ...
I get the impression that ...
The structure we must avoid is
In my opinion, war is always wrong.
He wrote about the war from the point of view of an ordinary soldier.
In my view, it's a very good school.
You have to judge a school from the child's point of view.
Self-study activity:
Get together with an English-speaking friend and express your opinions about the billboards that you can see after clicking on the picture below. Do you like the billboards? What products are being advertised? Is the design effective?
