Well, where to begin. The format was quite well set up, with questions sent in by members of the public (selected in advance by the consortium of broadcasters), on the economy, the environment, health, the arts, Afghanistan, the issue of trust in general, and the first issue that each would tackle as PM. (On the last point, Duceppe said something to the effect of "Well, I know I'm not going to be Prime Minister, and three of you won't either. Some of you know it.")
So how did they do? Well, nobody actually crashed and burned. Harper, though, came across as sickeningly smug, with a vile grin on his face of the type that makes you want to rub his face in the cat box. Harper also had this infuriating way of talking about almost everything in terms of marketing, as if good marketing is the solution to everything. He also seemed out of touch when he said "Canadians aren't worried about losing there homes and jobs, they're worried about their portfolios". Well, Steve, maybe that's true of the people you know...
Dion? Well, he exceeded my expectations. However, I don't really have much to compare with, not being a regular watcher of TV news. I read about him on the net and hear about him on the radio a lot, but I haven't watched enough footage of him to know if (a) he's improved the way he carries himself dramatically, (b) he never was too bad, but the media just got off on portraying him that way, or (c) he's still awful, but I'm too alienated from my fellow human citizens to see how poorly his style would go over on them. He would not commit to never running a deficit, whereas most of the others did.
Layton was extremely good at explaining his ideas in a clear fashion. He seemed to interrupt the others a bit more than most, though all of them did it occasionally. He was the first of the leaders to raise the impact of the FTA and NAFTA, and advocated immediate withdrawal from Afghanistan, then getting the UN in there in place of NATO. He was not explicit, however, on whether or not Canada should be involved in the UN mission that follows. He also did a good job of pointing out the main drawbacks of the Conservatives' approach to helping business and the arts using non-refundable tax credits, namely that they have to be redeemable in order to help those who most need them (who, after all, are below the threshold for paying income taxes, and would thus not benefit from non-refundable credits). He also pointed out the folly of Harper's cherished "intensity based" emissions targets (for instance, you could produce more oil from the tar sands as long as your emissions per barrel were lower, with the result that your overall emissions could, and probably would, continue to increase). He was not as explicit as he could have been in discussing the relative merits of cap and trade over a carbon tax. On the other hand, he pointed out one of the elephants in the room, namely the fact that the Conservatives have not yet released their platform. He said that an NDP government would not run a deficit, pointing out the fact that NDP provincial governments, contrary to stereotypes, have generally been good fiscal managers (and threw in the fact that the obvious exception, Bob Rae, is now a Liberal, for good measure).
May also significantly exceeded expectations. She handled herself competently and confidently, in stark contrast to the train wreck that one is led to expect when most of one's information comes from babble. She handled economic issues well; she mentioned that Canada is in danger of experiencing "Dutch disease", though it would have helped if she'd explained what it was rather than expecting the average viewer to look it up (pity you can't put hyperlinks in speeches). She was also the only one of the leaders to mention electoral reform among the first priorities she would address as PM. As many babblers predicted, though, I can't recall seeing her attack Dion once (though it's possible that I missed something, since I had a number of interruptions while watching the broadcast).
Duceppe was very good as well. In terms of presentation, he was perhaps the best of the five. I liked the way he remarked on the irony that he was the first to advocate a "buy Canadian" policy in the course of the debate. He was also the first to bring up First Nations issues, in the context of health policy. However, health was otherwise one of his weaknesses in terms of actual policy, given that he is a big-time decentralist, to the point of objecting to federal regulation of such things as privatization of health services (he says he doesn't advocate this, but it should be up to "Quebec and the provinces" to decide these matters). Similarly, he objects to national securities laws; he thinks that this should remain a provincial matter. These are understantable in the context of a Quebec nationalist, of course, but probably bad for much of Canada.
All in all, I'm happy I watched this rather than the Biden-Palin debate. I'm sure that anything really juicy that came from that debate will show up on YouTube anyway.