The problem is, we're in the age of the blockbuster as far as movies are concerned. That is, people expect major drama, huge special effects, etc.

The POV nature the books are written in are the biggest obstacle in my opinion. That would be difficult to get across, but it can be done, though I think you'd certainly lose certain things, like Mat's ancient memories, and the way The Forsaken recall how things used to be in the AoL.

As for the length of the books. Yes they are very long, but, how much of this is just description? We all know you can read for 3-4 pages in WoT without any actual dialogue, so the film maker would be able to speed things along to a certain extent.