Hehe, more seriously then - I don’t think one should make too definitive statements about something we don’t have any concrete proof of, and I’m definitely open to input from others (though I don’t promise I’ll listen…), but I definitely think you can say quite a lot about his playing from his character and the large amount of testimonies which have been penned down.
The first thing to note is that Liszt is perhaps the most universally admired and accepted pianist in history. By young and old alike, classicist to romantic, from Clementi and Cramer to Schumann and Rubinstein. There’s almost no controversy about him, which tells me that his playing must have been natural, intuitive and likely tremendously powerful - in some sense - and that he was not an eccentric pianist like Pogorelich, or one who easily divides listeners like Cziffra or Horowitz. To me, that means we’re dealing with something more akin to Richter, to Cortot (minus the wrong notes), to Volodos, etc. If you then look at how Liszt himself discusses music, it’s practically invariably the intuitive, spiritual side of it he brings up, which furthermore tells me he was more concerned with character, essence, analogy and the larger picture than details, art for art’s sake and pianistic craftsmanship. I think this is further brought out by listening to what the people who heard him choose to highlight from his playing. There’s never any talk about how he brought out nifty hidden voices etc, but you have people in the site here above talking about a dreamland you’d never want to leave, about how his feelings extended to the very tip of his fingers, about how all their pains were translated in to poetry, the instincts elevated, etc. This is not how you’d describe the young Pletnev for instance, or Horowitz, or Hofmann, Schnabel, Lhevinne, etc. Boissier’s diary from the early 30s also describe Liszt analyzing music almost entirely in psychological terms, I think it was Lachmund who summed up his playing as centering around mysticism, and Göllerich who philosophized about how Liszt drew the dark, contemplative tone from the piano in the final variations from Schumann’s Op.13. It’s again character, aura, symbolism, communication - it’s not about how he phrases melodies, brings out bass lines, created beautiful sounds or whatever. This is more debatable, and also something I think changed during Liszt’s life, but another thing relating to this I find interesting is that, in spite of Liszt’s by all accounts truly unbelievable technical prowess and the vehicles he composed to display it (which must have seemed like music from outer space to the audiences of the time), you hardly ever hear people rave about what blazing octaves he had, the speed of his runs, etc. It is there, and everyone alludes to it, but what they bring out first - before all that, and much more strongly - is the musical experience, which also leads me to believe he might not have been as obviously flashy as Cziffra for instance in his playing where attention is really drawn to the mechanical feats, but maybe more akin to a Richter type of pianist - who can be equally stunning - but where it’s more naturally embedded in the music.
Richter comes up a lot above - I don’t think Liszt’s playing would have resembled Richter’s a whole lot, but that is the name which keeps being a convenient example to use, and who I think in terms of “type” of the pianist Liszt would have resembled. I think Liszt was a completely different personality at the piano however, who likely was much more open, vivid, instinctive and “social” in his playing - but who nonetheless had a similarly magnetic personality, natural approach to music, and ability to lead his audience and transform the score in to soulful, deeply communicative and deeply powerful experiences for his listeners.
