So Elizabeth May is quite the spitfire. To bad her party is irrelevant, she'd make a good PM, she's intelligent, honest, and knows her material. She used the debate to push her environmental agenda and since it's largely a pointless exercise for her that's probably a good decision.
Harper was the best speaker by far but lost on just about every front. He's completely out of touch but given what he has to work with he held his own.
Mulcair started out looking like a deer in headlights and comes across a bit wax like (he's like that in person too, it's just his appearance), might be a robot, but also seems to be the most in touch and probably won on most points.
Trudeau is all flash, I think he might have killed some of the "he's not ready" sentiment the PCs keep throwing at him but he definitely didn't shine on the intellectual front. All of his shots were petty and shallow. There's no substance when he speaks. I don't know that he'd be a bad leader but he's not a great communicator (I'm making allowances for language as I don't care if the guy uses the wrong word now and then, he just doesn't get good points across.)