I think we won't know if 3.5 was/is a failure or not until 4E comes out. If WotC puts it out too soon, they'll face a real backlash (IMO). But if they wait, say another 5 years, then I think everyone will move on and forget about the 3.0 to 3.5 revisions.
How many people still play 1E? 2E? Not...