I know one of his major issues is how they handled Booster Gold, and how he's portrayed as much more incompetent than he should be, and as someone not too familiar with the character, that's why it didn't bother me, but I can see why fans of the character would be annoyed at his portrayal.
Same with the dark humour, I've always liked King's style of humour and the events in The Gift are so ridiculous I laughed really hard at it, but I can also see why it may be too much for some people.