According to their sources, the game will sport a higher resolution and UI:
Today, multiple sources with knowledge of Blizzard internal plans said that Blizzard will reveal StarCraft HD to the public this September. The StarCraft HD remastered version will retain the original gameplay and is said to have improved graphics resolution and user interface (UI).
The source that leaked the information points out that September lines up with the StarCraft II World Championship Series ending. More details will supposedly surface during BlizzCon this November too.
The extent of the remaster is unknown – meaning we don’t know if it will use 2D sprites like the original, or have polygonal graphics like its sequel.