Interesting, since it's the opposite experience for me ... bland Mozarts versus lively and varied Nielsens 
I have a very intense and long-lasting relationship with the Nielsen concerto - my life partner, you might call it. When I got my first clarinet, at the age of 15, I bought at the same time the piano edition of the concerto. I remember the assistant in Taphouse's in Oxford, who obviously knew his stuff, commenting "That's certainly something to aspire to, sir." Since then I've failed to master the solo part, and was recently within a few weeks of playing the snare-drum part in a concert, before the orchestra (not the soloist) got cold feet. I have also typeset the whole score in Sibelius, out of sheer fascination with it. I'm not suggesting for a minute that this gives my opinions of the piece any special status, but it does make me awfully hard to please with regard to performances. I think I have finally settled on my 2 favourites, so what I plan to do... sometime this year... is a Hurwitz-style review on this very forum (no video, don't panic, Hurwitz is George Clooney compared to me, I promise you) along the lines of BBC Radio 3's
Building a Library, comparing the available versions. I've just got a fair number left to listen to, after which pen will start hitting paper, or fingers keyboard.