He remained based in Europe throughout most of the 1990s, although he returned to the US in 1998 to appear as Ruggero in Washington National Opera's production of "La rondine", and increasingly assayed lyric tenor roles, singing as a guest artist at the Vienna Staatsoper, La Scala and the Opéra Bastille in Paris. From 2000, Haddock continued performing in Europe but increasingly appeared on North American stages as well. He reprised the roles of Ruggero in "La rondine" and Hoffmann at Los Angeles Opera, appeared as the Duke of Mantua in "Rigoletto" at Dallas Opera, returned to Washington National Opera as Cavaradossi in "Tosca" and Pinkerton in "Madame Butterfly", and sang Gabriele Adorno in "Simon Boccanegra" at Santa Fe Opera. His Metropolitan Opera house debut came in 2003 when he sang the title role in Gounod's "Faust" and appeared there later that season as Alfredo in "La traviata". His last performance at the Met was in 2007 as Gabriele Adorno in "Simon Boccanegra". In Europe his performances during this time included his house debut at Barcelona's Liceu as Alfredo in "La traviata", his role and house debuts as Don José in "Carmen" at Glyndebourne, and a reprisal of Gabriele Adorno at London's Royal Opera House in 2008. Haddock retired from the opera stage in 2009. He was preparing to leave for a series of opera engagements in Europe in March of that year when he suffered two massive strokes in 24 hours at his home in Skaneateles, New York where he and wife Kathleen had settled in the late 1990s. The strokes left him partially paralyzed on his left side and also affected his voice. After three years of rehabilitation, surgery, and physiotherapy, he began a new career as a voice teacher. He initially taught in his private studio in Skaneateles and at Hobart and William Smith Colleges. He continues to teach at his private studio and at Colgate University. Haddock's full-length opera recordings include: