The American remake is better because of one key element. SPOILER ALERT.

In the American adaption, we see Owen, the young protagonist, find an old photo of Abby the vampire and her protector from decades ago when the protector was a young boy the same as Owen is now. This is an omen of what will eventually happen to Owen; he will age into a duplicate of the protector, a pathetic elderly, obsessed man murdering innocent people to appease his child-like vampire mistress.

This is missing in the original Swedish film. We assume Hakan is just some pedo that Eli recently convinced to help her and that Oskar and she will go off and have a happy life of fun vampire adventures together.

Without this old photo the story is just the author's personal childhood fantasy of having a cute vampire girlfriend to protect him from bullies. With the finding of the old photo, it becomes a genuine horror story about how a lonely, misfit young boy is groomed and seduced into becoming a monstrous slave to an ageless, evil being.