I think most GTA IV fans know that overall people didn't like the mature direction
See, this is the problem.
The problem with fans like you that idolize IV so much that makes ( or want to turn a blind eye? ) you blind to the actual reasons behind criticisms, and keep making silly threads like these for simply passing the blame on others who disliked the game, including the kids whom people like you find so young and immature that they can't understand the story simply because of the "serious and mature" direction despite the fact that there are similar games ( like Mafia 1 a lot mire realistic than IV, as well as gritty and mature ) which managed to appealed many young players.
The issue isn't with the mature and serious direction. The differences lie in how both IV and Mafia 1 execute the mature themes, and handle the storytelling taking the realistic, serious approach in addition to lots of attention to details to make the overall experience highly immersive and memorable.
The differences are explained many times so I'm not going to repeat again, and again, knowing that you have clearly comprehension issues even after making you realize many times about the same, which explains why you always foolishly point fingers at players for rejecting IV rather than understanding the actual issues.
It has nothing to do with the mature / serious direction nor the kids are to be blamed.
IV simply sucks at being fun, feels a lot boring with all the errand nonsense and a muddled, meandering plot with an approach so cliche in typical GTA fashion instead of actual maturity and serious treatment.
It could be better and IV does show a promising change for the future only if R* really knows how to handle it, just like the creators of Mafia 1 knew and did superbly.