Dion's shortcomings are too numerous to count. I will limit my comments to three.
One, his English sucks.
Two, outside of Quebec this loss has a lot to do with Dion. The Liberals were never able to shake off talk of 2008 "coalition" that Dion put together. The Liberals were the party of national unity until Dion decided to form a non aggression pack with the Bloc! Stupid stupid stupid.
Three, while the Liberals actually did a nice job boiling down what the Green shift was ("Less on what you earn more on what you burn"), the Liberals were never going to be able to explain to the public just what is "burnt" and as a result how such a shift would effect the cost of any number of goods and services. The Conservatives gave them an answer. It would be a "tax on everything". Naturally some Canadians were convinced that this was simply a tax increase in disguise. But the kicker was this. I do not care what Canadians told polling companies about climate change. No one I mean no is ever going to be excited over a tax shift. Making the central plank of his platform something that did not offer a single tangible benefit Canadians just went to show how hopeless Dion was as a politician and why he needed to be ushered out the door as soon as possible.