It’s clear that Sisters put in considerable effort. Tina Fey and Amy Poehler have a natural rapport, and some of the film's strongest scenes arise from their connection. However, the movie frequently doesn't quite succeed. The humor largely relies on awkwardness. The plot involves characters repeatedly doing mortifying things. While this kind of comedy can be effective when handled skillfully, Sisters seems to relentlessly apply it until the effect is lost. This approach feels unexpected, and so does the frequent use of crude and sexual jokes. There are some genuinely funny instances involving these elements as well. Ultimately, the problem lies in how the movie was constructed; it gives the impression that the writers had a checklist of "funny" scenarios they wanted to include, attempting to force them into a basic storyline. This strategy of trying everything to see what works inevitably results in a lot of material that simply doesn't land.

Source on TMDB