Incomplete doesn’t mean invalid, though. I can say I didn’t enjoy the first half so much that I didn’t give the second half a chance. I will have enough information to explain why I didn’t enjoy the first half and my opinion of the movie is completely valid.

I don’t have to continue to subject myself to something I don’t enjoy. I can explain what I don’t enjoy. People don’t need more than that to have a valid opinion of something. The only people I’d expect to have done more is somebody professionally critiquing movies.