"I have not watched this film yet."
Translation:Jeszcze nie oglądałem tego filmu.
If you say "nie oglądałem", it's a general statement that you just haven't watched it. If you say "nie obejrzałem", it suggests that you were planning to do so, or that your interlocutor expected you to watch it.
One could argue that "nie obejrzałem" makes more sense with 'jeszcze', although frankly this here sounds ok to me as well.