Why did the movie Mame get such bad reviews?

I had heard negatives from reviewers of the musical rendition of Mame. With the wonderful music of the show, Lucille Ball, Bea Arthur, and Robert Preston as the leads, I simply could not imagine it would be bad so out of pure curiosity I watched it last night to see if I agreed. I enjoyed most of it. Liked the first half better than the second. Certainly do not think it was the best movie musical out there, but I absolutely do not think it deserved the low ratings it got. I thought Lucille Ball and Robert Preston were great. Overall, very entertaining and I thought the scene in the middle of the film when they sing "Mame" is wonderful. Just wondering if anyone out there agrees or if you disagree and feel I missed something, I'd love to know.