I just wanted to shamelessly plug our project in here. I'm working with a few other guys to reproduce the SC and SC:BW campaigns in the SC2 engine with a few tweaks like added difficulty and expansion units available in the earlier episodes. Don't sweat the lore too much.
It got featured on TeamLiquid, GosuGamers, and even HuskyStarcraft, who's currently doing kind of a Let's Play of it. If you haven't played it or haven't heard of it before, you can check it out and download it from the project pages:
SC1 Episode 1 - Rebel Yell - StarCraft 2 Maps - SC2Mapster.com
SC1 Episode 2 - Overmind - StarCraft 2 Maps - SC2Mapster.com
The Protoss campaign is currently in development.
If you have any thoughts, suggestions, feedback, bug reports, compliments, complaints or whatever, please post them here.