Here are some examples of Litvish gedolim saying positive things about Rebbe Nachman of Breslov and his works (taken from a Breslov website):
Rabbi Yisroel Meir HaCohen, author of “Chofetz Chaim”: “If you wish to draw close to Chassidism, draw close to Breslov. They keep and follow the Shulchan Aruch.”
The son of the Chofetz Chaim acustomed himself to praying with Breslover Chassidim in Warsaw.
Rabbi Yaakov Yisrael Kanievsky, the Steipler Gaon: “This book (Likutey Moharan) stirs me to fear of Heaven. And, I see that if there is a day that I don’t learn this book, I feel lacking in Heavenly fear.”
Rabbi Chaim Shmulevitz, Rosh Yeshiva of Mir: “Through (learning) Likutey Moharan, the mind is opened.” He also said “We work on trying to solve problems (in scripture) and they (Breslover Chassidim) work constantly on ‘fear Hashem and love Him all your days.'”
Rabbi Avraham Yeshaya Karelitz, author of “Chazon Ish”: “The light of lights of truth…” Rav Ben Tzion Apter said that here and there the Chazon Ish would speak to him about the strenght and greatness of Rebbe Nachman and each time would say “tell over a teaching of the Rebbe.”
Rabbi Elya Lopian on Rebbe Nachman’s books: “These are real books of ethics.”
Rabbi Eliyahu Dessler, author of “Michtav M’Eliyahu”, quotes from Rebbe Nachman in his books. In a letter to his children, he encouraged them to learn Breslov works in order to merit fear of Heaven.