There is a harpsichord cadenza that lasts almost a full five minutes.
Rather than the uptempo finale that one would expect in a final movement, Beethoven substitutes a Minuet/Trio dance movement instead.
The final movement includes a choir and four vocal soloists in addition to the full orchestra.
In addition to playing in the traditional manner, members of the orchestra are required to make all kinds of extramusical sounds (e.g., whispering, stamping their feet, string players playing with the wooden side of the bows, etc.).