I would agree that the first movement is the most difficult, but not from a technical standpoint. There are so many moments that remind me of someone running up to a cliff full speed, then stopping abruptly and they are teetering over the edge... so many build ups that lead to a subito piano... really difficult to pull off.
In addition to the overall dynamics, voicing, balance in the first movement... there is the part where the left hand has the triplet repeating 'C' in the bass, and the right hand has to beast through the first theme entirely on its own.. now THAT was awkward to get going.
The second movement is tough because it starts out as a slow movement, but builds up the pace throughout the variations; it's got quite a bit of finger work near the end! Don't underestimate this one.
The third movement is a study in dexterity; there is a part in the middle where the hands are kind of playing in canon... that's the toughest part for me; or in the recap when the left hand takes off with the theme in 16ths and the right hand accompanies.. fast passagework in this movement is hard enough for the right hand; having to suddenly take it with the LH and have it cut through is tricky.
Overall, this sonata is a beast. The first movement took me about as much work as the second/third combined, just because it's so damn dramatic! The first page is full of angst, and you need to project this sense of urgency with all the shifts from minor/major. It's just overwhelming the amount of detail Beethoven put into this movement. The first arpeggiated thing for the right hand is just like lightning out of no where. It's the first virtuoso moment, and those low chords that follow it just hit you hard haha.

I'm rambling, but mostly reminiscing at the amount of insanity I discovered within the piece. So ya, it has a lot of technical challenges, but the only REALLY awkward stuff for me was the Th1 in right hand with the repeated notes in the LH (recap of movement 1). That just really didn't fit nicely (the trills were atrocious here); The rest just took time and slow practice.