Who could do Dirty Harry justice today?
They'd have to have the look, coolness, and be more on the political right to pull if off and have a fan base. Plus, several things aligned like director Don Siegal, awesome MAJORLY IMPORTANT score (Lalo Schifrin: Bullitt, Mission Impossible), combined with Eastwood. It mirrored the alignment of The Good, the Bad, and the Ugly with great director Sergio Leone, great composer Ennio Morricone ... waa waw waa, and Eastwood.
Initially Sinatra was already set to play DH but had recurring pain from a previous on-set hand injury and couldn't hold a gun. It would have been different on a lot of levels: New York City setting, different composer, etc.... and very likely not nearly as good.