he is much more unlikeable in them apparently.
I wouldn't say he is more unlikeable in the books, but he is definitely more complicated.
For starters he is 20 years younger. He comes across at first as like a typical playground bully who lashes out verbally and physically to cover up a cripplingly low self-image. He is an utter gob-shite and 99% of everything he says is utter bullshit. Interestingly, the two people who see straight through it are Sansa and Arya. In the books he is not a point-of-view character and you really mostly 'see' him through the eyes of the two Stark sisters - both of whom see him through a filter of their preconceived ideas.
In the show they have massively downplayed his interactions with Sansa and massively exaggerated his relationship with Arya. In the books, he is pretty much a broken man after the red wedding and wanders the Riverlands aimlessly with Arya - having little or no conversation with her. He tries to get work in a village building a palisade fence, but once he's finished the heavy work the villagers church him out as they don't want to be sheltering 'Joffrey's dog'. His final undoing is when he goes to the Inn at the Crossroads and finds out that Sansa has been married to Tyrion and gets so pissed he can't fight the Tickler and Polliver properly and sustains a leg wound which gets infected. Arya leaves him under a tree (like in the show) and goes off to Braavos. No great chicken speeches, no fight with Brienne.
In the books there are some brillinant (and cringeworthy) interactions with Sansa. She shows great empathy towards him and is able to instinctively respond to him in a way which calms down his most terrible rages. Although I can understand why the show went a different path (it would have made him look awful as a character) it has detracted significantly from showing her character development and her better personal qualities.
Most annoyingly, two of his finest moments with Sansa were robbed from him and given to Littlefinger, of all people. In the books it is Sandor who tells Sansa the story of his scars. In the entire book series she is the only person who knows. Also, he said the line 'they're all liars here, and all of them better than you'. The significance of the scene in the books is that it sort of sets him up as being the Lady replacement for Sansa, which may yet come to pass in the books. However, that's still just a theory.
As I said before, Sandor Clegane is a bit of a 'specialist subject' of mine and I could waffle on for literally hours about him. He is one of my favourite characters, and I think he's one of GRRM's.
When he started writing the series, GRRM said he would envisage Ron Perlman playing the Hound. Ron played Vincent in the 1980's series Beauty and the Beast which was written by........GRRM.