tough act to follow
so good that whatever happens next is not likely to seem as good.
The last mayor was one of the most beloved in the city's history, which means Mike Ransom has a tough act to follow.

[TahlilGaran] English Idioms Dictionary ▲

tough act to follow
n. phr. A speech, performance, or activity of such superior quality that the person next in line feels and thinks that it would be very difficult to match it in quality.
Sir Lawrence Olivier's performance of Hamlet was a tough act to follow in every sense.

[TahlilGaran] English Idioms Dictionary ▲