The Terrans of StarCraft have always held a special place in the heart of players, and former players will feel right at home. You can still pop some Stimpacks on your Marines and fill Zerg full of holes before they even reach you. You can still unleash hell from miles away with Siege Tanks. The mighty Battlecruiser can still create big gaping holes in opposing defenses and capital ships with the Yamato Cannon.
Aside from these iconic units, the rest of the Terran forces are new and unique in some way, and you'll have to come up with new tactics and strategies to put them to good use!