I would never say that Spike/Buffy was the greatest love story though, because I felt it was more of a portrait of the most self destructive relationship you could think of.
It made what happened when Spike got his soul even better, because then it was the ultimate sign of wanting to make things better.
We can debate on whether Spike really wanted his soul back or not, but I think the demon who did it was supposed to be looking into Spike's "heart" and seeing what he "really" wanted.