(SPOILER)Tidus obviously despises his father during the game, simply because he thought Jecht treated him in a very bad way.
However, I actually think Tidus should grow some understanding for his father during the plot.
At one point in the game, Auron explains to Tidus that Jecht did love him and didn't know how to express it, and Tidus thanks Auron for telling him.
He also sees this Sphere recording where Jecht tells Tidus how he believes in him, and there's also the scene when he asks Auron to look after his son.
In spite of this, Tidus keeps hating him, and I actually think he should develop some kind of understanding after all those events.
I understand that these things are hard to get over, but still...