Being a massive warcraft II, and warcraft III fan, and reading many a novel, I'm excited and worried for this movie for two reasons.
One the story telling is immense, however it's not cut and dry. I'll give a quick "overview" of the story.
In warcraft I - its orcs vs humans, the orcs have invaded azeroth to take it over. Orcs are seen as bad guys. just one city they were looking to take over.
In warcraft II - Orcs vs humans again, this time a much larger army, and more orc clans are involved, this time looking to take over basically everthing in the world of azeroth.
In warcraft II : expansion - the humans have pushed back the orcs, and now push through the dark portal (where the orcs came from.) into the orc world, and look to eliminate the orcs..they fail miserably.
warcraft III : the portal is closing, and draenor (the orcs world) is getting destroyed the orcs have no where to go except through the portal back to the human world to survive. The orc clans get scattered, orgrim doomhammer who was the warlord in Warcraft II, is no where to be found, Thrall is born, and raised by humans to be used as a gladiator, eventually, realizes he is an orc, and rallies the orcs by breaking them free from internment camps. Thrall is the new leader, eventually finds another continent called Kalimdor where the orcs can live away from humans.
Finds out the whole reason this war started, was because of demons that were looking to enslave both races (human and orc) to battle the nightelves. The orcs were brainwashed with bloodlust, hence the first two games were human vs orcs, and an orc had made that pact, along with the guardian of earth (medihv.) Demons defeated at the end by all the races rallying against the undead scourge.
warcraft III (expansion): the undead are rallying, under a seperate leader, and seem to have gained self awareness, humans and elves look to stop this from happening. Orcs just enjoy there life on kalimdor, but get attacked by humans for being orcs basically.
This ends up ending with the undead all being under control by a former human prince who went corrupt, and turned undead.
Then WoW starts..and you have all this other lore.
This is why I have no idea if they start from the beginning, or if they jump right in. I really do hope its the beginning, because there's obviously a lot more deeper stuff that happens, crazy twists and turns, very games of thrones-ish, when you hear the different sides points of views.
Hope that helps anyone whose interested to get just a bit more excited for this!