I don't know very much about George V, but I have always had the impression that he was all considered a good king. Indeed he reigned in a very difficul period, but I never heard complaints about his reign.
And regarding his bad relationship with his sons, well, I think that he treated them in the same way he felt his own father had previously treated him; also Prince Albert (and Queen Victoria) had difficult relations with Edward VII, and Edward was definitely an inattentive husband and father in Victorian period, when children education was all but soft.
Edward VII was far closer to his son than George V was to his because Edward wasn't anywhere near as strict with his children as either his parents were with him or George was with his sons.
George V has a couple of conflicting comments on this issue.
1. He described his relationship with his father (after his father's death) thus: I have lost the best of fathers and my best friend.
2. He is also supposed to have said: My father was scared of his father, I was scared on mine and I am damned sure that my sons will be scared of me.
I do believe that the latter comment was said while his sons were young whereas the earlier comment was said when he was an adult.
He certainly had a great relationship with his father as an adult with some people saying there were more like brothers than father and son.
George V was a canny politician as seen by the fact that when all the other monarchies were falling he made the hard decisions and kept his throne and that includes the decision to not allow his beloved cousins Nicholas and Alexandra and their children refuge in Britain. He did, of course, later on ensure that another first cousin, Prince Andrew of Greece was able to escape from Greece with his wife and children, including his future grandson-in-law Prince Philip.
I think, at times George V is compared unfavourably to the glamour of his father's reign but isn't given the credit for being the inspiring King he was during WWI, just like his son was a war later. Britain wasn't bombed as heavily during the first war but London certainly was bombed and he also visited the troops regularly, had sons serving but also had the family concerns about his cousins and other relatives serving in other countries.
He has been a favourite of mine.