Beethoven is often technically difficult, so that's one hurdle. He is often profound in the emotion he evokes--capturing it is not so easy, especially if you are still having the slightest technical problem. His music is often rather exposed, such that you must be exacting in your playing--you can't hide anything in a jumble of notes and still have it comprehensible. You can't be overly sentimental (a la Liszt), yet too reserved an interpretation leaves Beethoven sounding strangely unmoving.
As someone who just played the PC 4, believe me, I struggled with all of the above. I haven't come close to my ideal performance--but at least I feel closer.
Despite all the difficulties, the most important point is the greatest redeeming value of learning Beethoven--you feel seriously ONE with the universe when you pull off a decent performance!
have fun!
Teresa