This is one of the most exciting things I've ever played! It's perhaps interesting to know that Rachmaninoff actually composed two cadenzas for the 1st movement and many pianists prefer the ossia version; yet I think that this one (the one here below) is more original and light and, most importantly, allows for a more convincing crescendo. Here is what Geoffrey Norris has to say on this (excerpt taken from his excellent book on Rachmaninoff):
"Rachmaninoff composed two versions of the first part of the cadenza. One is 59 bars long with an intricate passage work; the other has 75 bars, is chordal throughout and is considerably more taxing (...) The numbering of the pages in the manuscript indicates that the longer cadenza was the composer's first choice, but presumably the necessity to fit the concerto conveniently on to 78 rpm records compelled him to choose the shorter one, or maybe Rachmaninoff simply felt that enough power had been generated elsewhere and that lightness provided an agreeable contrast. Both versions achieve the same purpose in providing a suitable platform for displays of virtuosity and in commenting adequately upon the motifs from the first subject".
I am not convinced that the longer version was the composer's first choice but it's of no importance really.
So, here is an excerpt from the [short] cadenza (I had to stop when the orchestra comes in, for obvious reasons!).
Any comments are most welcome!