I think putting it in a movie format was fine. I feel making it into a tv show would either make it a bit too boring or way too much cliff-hanger each episode before the next one will be aired.
It was a fun murder mystery movie to watch. The whole first half of the movie was the build-up and the second half was fun to watch how the murder was resolved.
Branagh did a wonderful job, and I really liked the character he portrayed. So funny.