He was a cosmopolitan in the best sense: born in Schenectady, NY, raised in Australia, working in London, and at home in all senses of the word, in Czechoslovakia and Czech culture. I will miss him for his interpretations of both Czech works and music of the Classical era alike (some of which overlapped). He is perhaps best known and will be best remembered for the former, but it would be a shame were we to neglect the latter.
Although I have always been a devotee of so-called early music and the classical repertoire played on period instruments, being a historian does not mean being an antiquarian, much less abandoning the critical spirit. I myself was drawn to performances on early/authentic instruments because I wanted to hear what the sounds of the time were like, and knowing the constraints of the instruments further helps us to understand how the music was composed and played. This would be a long discussion, so suffice it to say that, as Richard Taruskin and others have not ceased to point out, the idea that we can achieve an objectively "authentic" performance is a fantasy for a variety of reasons, and poorly conceived performances on period instruments can be as deadly in their way as overblown modern ones.
Mackerras represented that ideal combination of originality and common sense. He realized, for example, that what really mattered were authentic performance styles and techniques: properly employed, smaller, historically appropriate ensembles, and period performance practices can be refreshing and revelatory, too. It was thus precisely refreshing and revelatory to hear him conduct not just forgotten gems such as the symphonies of Voříšek and Arriaga, but also the standard repertoire by Beethoven, Mozart, or Brahms. In the end, though, he remains, for me as for many others, inseparable from Janáček.
Jessica Duchen's music blog almost immediately came out with a fine tribute, and she concisely sums up his legacy:
Celebrated for an exceptionally wide range of achievements, from championing Gilbert & Sullivan to pioneering the slenderised sounds that mingle period-performance-practice with modern instruments, from working with Benjamin Britten to resuscitating the reputation of Janacek almost single-handed, Mackerras has made the impact of a musical meteorite.The piece includes video of an interview (which shows his appealing modest and sense of humor and provides some information on his instrumental training and his early connections to Czechoslovakia when he studied under Václav Talich).
And, from NPR:
• Tom Huizenga, "Conductor Charles Mackerras Dies at 84" (Mackerras Conducts Janacek with audio of his performance of 'Kat'a Kabanova')
• Tom Huizenga, "Charles Mackerras Played My Wedding"