SC1 had a great story with excellent writing, especially for the time. SC2's story was schlocky garbage. The biggest example of this is the opening cutscene of 2 with Raynor in the bar.
Raynor's literal final line to Kerrigan in SC1 was "It may not be tomorow, darlin', it may not even happen with an army at my back. But rest assured; I'm the man who's gonna kill you one day. I'll be seeing you." Meanwhile in the opening cutscene of 2 he's pining over an old photo of her before she became a Zerg. Mind you any romantic relationship between Raynor and Kerrigan in SC1 was only possibly hinted at, it was never explicitly established.
Also they literally never even mentioned Fenix, Raynor's best Protoss buddy, in SC2 Wings of Liberty despite Kerrigan betraying and murdering him.
Raynor's literal final line to Kerrigan in SC1 was "It may not be tomorow, darlin', it may not even happen with an army at my back. But rest assured; I'm the man who's gonna kill you one day. I'll be seeing you." Meanwhile in the opening cutscene of 2 he's pining over an old photo of her before she became a Zerg. Mind you any romantic relationship between Raynor and Kerrigan in SC1 was only possibly hinted at, it was never explicitly established.
Also they literally never even mentioned Fenix, Raynor's best Protoss buddy, in SC2 Wings of Liberty despite Kerrigan betraying and murdering him.