I don't agree with most of the people who have a kneejerk reaction with the ending. I still think HeartBeat was good, but they chose to play the story straight instead of jumping the shark. This is, frankly, one of the few series where I'd have preferred the writers jump the shark to give the leads a happy ending, because they deserve it.

This series has one of the best written leads in K-dramas. Both In-hae and Woo-hyeol are absolute green flags, and they keep proving it over the course of the series. Their romance was of a slow-burn nature, built on understanding and wonderful communication. As a template for a great romance, their relationship is truly inspirational.

I do understand that most viewers aren't masochists. One of the worst mistakes that this series made was to market itself as a romcom - and while it was so over the first few episodes, it never really went away from reality. There's always human reality peering into their romance, even though it slowly and organically developed. The fundamental problem, I think, is with that dilemma that Woo-hyeol finds himself in, there's really no easy solution aside from leaning into even more fantasy, which might be tonally inconsistent with the series, but ultimately more sensible as it was branded as a romcom in the first place.

I do think that the ending is slightly more positive than what people think, because to me, Woo-hyeol returned to In-hae as a ghost (haunting only her). It doesn't change the fact that she's still human, but I think In-hae would be smart enough to have Woo-hyeol be exorcised as she'll be nearing her death (or ask help from the other vampires).

As a medical doctor, all realistic solutions fail because In-hae's blood would have to be sucked dry, and that will definitely kill her. I was hoping for some loophole that would allow them to do an exchange transfusion of sorts, but then that would take too much time and detract to the story. A more sensible solution (in terms of writing) would be for the curse to lift from Woo-hyeol as he showed an act of sacrifice for Do-sik's sake, perhaps reordering the world for the better. However, they chose to stick to their guns, which highlighted a pretty sad ending.

I'm still looking forward to picking up more clues with re-watching Heartbeat (as I have done so), but this remains to me a good series damaged by tonal inconsistency and a sad ending.