The only reason why people say "I liked Will Ferrell up to <insert movie here>" is because he does the exact same shtick every show and movie. So when people say that movie, it is because they finally had enough of it. Will Ferrell hasn't changed and I don't think is capable of change. Before anyone pipes up with "Stranger than Fiction", that movie was god awful and not a good example to use of praising him.
For me, it was Old School. It was a decent movie but I had my fill of Ferrell after. Brief watchings of Anchorman, Stranger Than Fiction, Talladega Nights, and Semi Pro confirm this theory.