His criticism of String is long and many-sided. I could not summarize it. It goes on through the video segment #7-#9.
His criticism of Loop---I mean mainstream Loop cosmology as practiced by his friend Ashtekar---is based on the second law. This is a serious issue. In Loop cosmology the bounce finding is generic---they try all the variations they can think of and they still get a bounce. So a pre-bang universe collapses to a critical density and then triggers a period of inflation.
Penrose does not like the conventional inflation scenarios and he sees violation of the second law in the bounce. He explains all this wonderfully with his handdrawn slides. Even if one already understands without watching the video, one could watch just for fun.