You can drink your Boulevardier like a Negroni with Rye, Campari, Italian Vermouth to almost equal parts.
Or you have it like a Manhattan: The Rye is the drink's core. It is supported by the vermouth and the Campari just works like a cocktailbitter.
Both drinks come chilled and are ready to drink. No extra ice needed. But of course it looks lovely, especially with the Negroni style.