I disagree. 2004/2006, yeah. But I don't think this election was a referendum on W; McCain was doing well enough until the economy tanked. I think it's a referendum on Republican Party more than anything. It feels like this frustration goes beyond just the President.
I can see how it could be a referendum on the Republican Party, but that doesn't really stand up to what happens in the primaries. After all, conservatives didn't nominate McCain, moderates, but mostly democrats who went out to republican primaries did. McCain rarely, if ever, got pluralities with people who identified as conservatives. Furthermore, the Obama camp's tactic of absolutely tying McCain to Bush with kevlar ropes is doing the best. Well, that and the economy.