Via Wikipedia

In general the symphony is sunny and cheerful, with light instrumentation that for some listeners recalls the symphonies of Joseph Haydn, with whom Beethoven had studied a decade before.[13] In a commentary on the symphony Grove comments that Haydn – who was still alive when the new symphony was first performed – might have found the work too strong for his taste.[2] The Fourth Symphony contrasts with Beethoven's style in the previous Third Symphony (Eroica), and has sometimes been overshadowed by its massive predecessor[n 4] and its fiery successor, the Fifth Symphony.[2]