No doubt Frank Sinatra was a talented actor as well as a talented singer. After all, very few actors nowadays can get a scene just right in one take, and that was pretty much Sinatra's modus operandi on set.
I feel that as the 1960's wore on, the quality of the man's films really started to tank. The Tony Rome detective series was nothing short of trying to compete with Dean Martin's Matt Helm series which came out at the same time. Perhaps even a James Bond competition, but nothing really worked for Frank during these years. His personal life in shambles, his music fading out...Sinatra appeared more like a throwback to the 1950's. The last great Sinatra film of this period was probably Von Ryan's Express in 1965.