For those say the ending is pointless, let me explain.
A lot of people say how Dennis ending up being a vampire ruins the whole point of the movie, which was accepting someone for who they were. I feel they missed a few points.
First off, Drac wasn't the only one who wanted Dennis to be something he wasn't. Johnny's family, though they didn't play that big of a role, wanted him to be human. Johnny was fine with who and what his son was, and so was Mavis, but Mavis felt the need to protect him from the world, much like her father did her. She assumed he was a human and didn't give him the chance to be anything else. This was a point Johnny tried to make during the big family fight.
Drac wanted Dennis to be a vampire, but he was pushing to hard, wanting to believe he was a vampire. He did this for 2 reasons. 1) Most parents/grandparents want their children/grandchildren to be like them. 2) He didn't want to lose his family because then he'd be all alone. This was even addressed in the film. He knew that if Dennis was human, then Mavis, being as overprotective as she was, was going to move to a "safer" human community, and he didn't want to lose his family. He believed Dennis was a vampire and felt the need to bring out his vampirism before Mavis moved them all away.
With Mavis, though she didn't care whether her son was a human or a vampire, she believed he was human, and felt the need to protect him from everything. She devoted all her time to keeping him safe and treating him like a human that she even neglected Johnny. She was never giving her son the opportunity to be anything more than what she thought he was because she was so concerned for his safety. In a way, she followed in her father's footsteps with how much she was trying to shelter him. She felt the need to get him away from the monster world for his own safety, but she didn't realize that Dennis, even though he seemed to be human, wasn't going to be able to fit in with other humans because he wasn't like them (this was emphasized by how the other kids treated him). But once Dennis revealed he was a vampire, she no longer had to be so overprotective, and thus could spend more time with Johnny, whom she had been neglecting because she was devoting all her time to keeping Dennis safe and working around a human schedule.
As for Johnny. While he didn't play as big of a role in this film as he did in the others, he still had a part to play. First, lets start with the fact that he had become what they call (excuse my terminology) p*ssy-whipped. Mavis obviously wore the pants in their relationship. Even Drac commented on how Johnny was being a wimp. And Mavis being so overprotective of their son took away time for them to be together. Basically, Johnny wanted his wife back, but she was dedicating all her time to sheltering their son and working around both a human and vampire schedule. Actually, one of the reasons' why Johnny was so submissive to her was probably BECAUSE she was so overprotective. There was really no arguing against her protective nature, so he never spoke up, not even when she wanted to move away and he wanted to stay. He eventually did though during Dennis' birthday party, and I also think that the way he showed up to fight at the battle (though it was already over) was meant to imply that he either found his balls or was willing to step up when he needed to, even if he didn't stand a chance.
As for Dennis, neither Drac or Mavis asked him what he wanted. This seems to be the part that everyone who complains about the ending missed. Drac was trying to get him to be a vampire, and Mavis was treating him like a human, but being far too protective about it, essentially smothering him. Dennis just wanted to be himself and stay at the hotel. But Drac was pushing him to become a vampire while Mavis was sheltering him. Drac's antics kept putting him in danger and frightening him, and Mavis's protectiveness was not only preventing him from reaching his potential, but also grouping him where he did not belong or wanted to be (hence why he was teased by the human children). It was Dennis who had to find out where he belonged. He wanted to stay at the hotel, and with Winnie, but it wasn't until he was at risk of losing both those things that he found the strength to fight for what he wanted.
In the end, it was Dennis' choice. Like his father, he wanted to stay at the hotel, and he wanted to be a vampire, eventually getting what he wanted. When it was all over, everyone got what they wanted. Drac got to keep his family together, Vlad came to accept humans, Johnny got his wife back and was able to stay at the hotel, Mavis no longer needed to be so overprotective and is now able to spend more time with her husband, Dennis got to be a vampire like he wanted and stay at the hotel and be with Winnie, and Johnny's family came to accept monsters.