Neal Ascherson did a good review of a Trevor-Roper biography in the LRB a while back that discusses the man's strengths and faults. The first paragraph summarizes it pretty well:

Seven years after his death, Hugh Trevor-Roper’s reputation is still a cauldron of discord. He would have enjoyed that. Steaming in the mix are the resentments of those he expertly wounded, the awe of colleagues at the breadth and depth of his learning, dismay at his serial failures to complete a full-length work of history, delight in the Gibbonian wit and elegance of his writing and – still a major ingredient – Schadenfreude over his awful humiliation in the matter of the Hitler diaries.

He once famously remarked that, rather than standing on the shoulders of giants, modern scholars were standing on little molehills, jealously guarding them. He was very good at critiquing those molehills, but he never managed to build a significant one of his own....which of course is a problem for most scholars- mastering your sources for more than your specialty can be difficult, and writing without doing that is dangerous, and he wanted to range pretty freely over the historical landscape and use his immense intelligence to jump to clever conclusions- which is why he was taken in over the fake Hitler diaries.

Still, there are some really very clever little things- his book on the forger Edmund Backhouse, The Hermit of Peking, is a gem.