Well I think WoL is supposed to have this undercurrent of 'will he actually go through with his promise to kill her'. And it's supposed to be subtle, it's just so subtle it's basically not even there.
And then in Heart they threw in that stupid 'you swore to kill the Queen of Blades' line, just to appease the fans. It wasn't a natural moment in any way shape or form.
Raynor and Kerrigan were obviously supposed to have a connection, and I think they had some feelings for each other. But this whole intense, soul mate romance is just... it doesn't make any sense. They probably knew one another for all of a few months at most. And even before becoming the Queen of Blades Kerrigan was a ruthless rebel assassin, and Raynor is a small-town Marshall. They're from totally different worlds; he doesn't and couldn't understand who she is at all. And that's BEFORE she became an infested galactic overlord.
Like it's an interesting story, but it had it's place. And it massively oversteps it's bounds in Wings of Liberty and it's even worse in Swarm; it's the primary character's entire motivation and it just doesn't work.
Plus it's so frustrating because a major theme, Kerrigan's whole arc in Brood War is that she's evolved beyond her human connections. But they just hit the reset button on that in SC2.