I'll chime in to say that this piece was surprisingly non-difficult technically. In fact, the hardest-sounding parts to me ended up (mostly) being the easiest.
The one place where I still struggle is just a bit before the "cadenza." The right hand states the United Airlines theme twice, and the first one is a real bear. The left hand has to make these weird jumps, in time, while the right smashes out the melody and then drops that delicatle little high figure in. From there on, though, it's very playable.
Gershwin, in my opinion from having played this piece, writes wonderfully pianistically.