Agreed, I really want to like the song, but his falsetto is terrible as you said. I usually love falsettos, too (Beach Boys fan here).I may not watch the films anymore, but I'm still quite familiar with the themes, and Writing's On The Wall is quite possibly the worst Bond theme ever. Bragging how it took 20 minutes to write and was recorded in one take is not helping. The fact that it's apparently top of the charts just shows that too many have their taste in their mouths.
It's not the lyrics or the music, it's the fact that they got a terrible singer for it, and that falsetto makes me cringe. /rant