I'm in two minds on this, if its really done well it could be fantastic top notch stuff that's going to propel WoW to new heights of success, but if its done badly then its going to be an painful to watch embarrassing pile of garbage that will hang around fan conventions like a bad smell.

Going on the history of 90% of fantasy films made being garbage I'd expect the latter, something of Lord of the rings quality would be positive for Blizzard, but judging by their in game movies (Chris Metzen is involved writing the script for this film according to this) then the stories there have moved to be more heroic comic book style which just isn't my thing.
They do mention there that they want a greater then PG tag so maybe they are aiming at the late teen sort of audience, but that doesn't match their younger player base.

My first problem would be that its a cartoon world, anything but a cartoon film is going to straight away look wrong and its stated to be live action. Still it'll be interesting to see what they come out with as they are trying to make a quality film (no Uwe Boll), and so are throwing the money at it.

So all in all I'd expect it to bomb.