I must admit I'm not too fond of that particular piece, I hope you won't hold it against me. I'll listen to Lewenthal's recordings of something I like more.

Just to be clear I really like Alkan's music I listen to him on a daily basis, what I meant was that to the common listener it takes a REALLY special performance to get them effectively hooked on Alkan with the exception of Le Festin d'Esope, Concerto, and Symphony.
It mustn't be 'dry' like how you would normally play a Hannon Excercise or a scale (though even these can be played beautifully). according to my knowledge there are sonatas by (I think) Scarlatti which have no dynamic markings in them, one could choose to play them like a machine and no one would like Scarlatti but pianists know better than that and fill them to the brim with musical expression and their own dynamic ideas and make fans of me and you.
With Alkan it's much much harder to do this, I think some people treat his music as a thing to learn the notes and play at speed, as something to show off with, a warhorse and this manifests itself in harsh sounds and sometimes dry playing. I listen to people play (even Hamelin) and I think sometimes they shouldn't have done that there or they could have played that differently, it may be that they are just following the score but it's not unheard of for pianists not to be 100% faithful to the score.
To answer the original question I say Alkan is VERY VERY difficult, it's one thing to play a piece through and an entirely different thing to make it sound beautiful. I hope I have made my point clear