The script is being penned by Charles Leavitt (Blood Diamond, The Express), but is being kept under wraps as to which WarCraft story it could be inspired from.
Lots of factors will affect the outcome of this being a great movie, but it is an "original" story for the big screen, so I am going to say yeah, I think it can be a great.
I have no idea what happened in the first two Warcraft games so any good story with orcs and humans could be a good Warcraft movie to me. However, if they decided to base it on Warcraft III then whoever is directing is going to have to be a genius to give me the same feels I got as Arthas slowly fell to the dark side
I'm not sure why Blizzard doesn't make computer-animated movies though, their cinematics are so epic!