General Tilney is accurately, if understatedly, described by Mrs. Morland as a "strange man" (29.10). Indeed. General Tilney is totally rocking out a whole Captain von Trapp vibe, from the first part of The Sound of Music before he became nicer and joined in the family sing-a-longs. The General is channeling the Captain from the period of the movie where he was overbearing, blowing whistles, and getting hung up on punctuality.
Like Captain von Trapp, General Tilney clearly runs a very regimented household, despite his efforts to appear laid back to Catherine. He's a stickler for punctuality. He's always getting mad at people for somehow disrupting his schedule or sense of order. And he's pretty much a jerk to his kids. Catherine notices these difficult personality traits when she is having breakfast with the Tilneys before traveling with them to Northanger Abbey:
Her tranquility was not improved by the General's impatience for the appearance of his eldest son, nor by the displeasure he expressed at his laziness when captain Tilney at last came down. She was quite pained by the severity of his father's reproof, which seemed disproportionate to the offense. (20.2)
Ultimately, the General is horrible towards Catherine. But this is only after kissing up to her when he thought she was rich. In fact, his attentions make Catherine feel uncomfortable. The General's behavioral about-face hinges on his knowledge about Catherine's personal wealth. The General is overly concerned with money, and ultimately proves highly judgmental and downright mean.
However, the General is far from a scary villain, despite the fact that Catherine suspects him of being a murderer or some sort of tyrannical fetishist who locked up his wife like Mr. Rochester, or someone in an Edgar Allen Poe story. When it comes right down to it, the General is kind of gullible. First the General takes John's word for it when John tells him that Catherine is rich. And then he believes John again when he insists that Catherine is dirt poor. Who actually just believes random, gossipy people, especially when they bluster about like John Thorpe?
In a way, the General is himself a parodic figure that completely disrupts expectations – both Catherine's and the readers'. Rather than behaving like the Gothic novel villain that Catherine believes him to be, the General behaves badly in a very real-world way. Granted, the General is not the sharpest knife in the drawer. And he's "strange," to put it mildly. But his motives stem from very realistic prejudices: namely, prejudices towards people with less money than himself. The General is a snob of the worst kind and treats those of a lower social standing than himself with disdain and rudeness. The General, and his outrageous behavior, are definitely a part of the book's comedic effect. But his behavior and attitudes also speak to social concerns that were common in Jane Austen's day.