Yes to the imperfection thing - which makes them much more human than many a supposedly human fictional hero. Ironic in a way that in a show about immortals they're really really human *g*
The thing I've always thought about Methos is that he's a kind of an oxymoron - on one hand, it's pretty much unimaginable what living for 5000 years would make a person into - IMO maybe a bit too alien concept for any of us, brief creatures, to grasp (and going on a tangent re: socipathic tendencies - maybe in a way, an ideal coping strategy for living so long and still being or seeming relatively sane) - and on the other hand, for some reason he often seems the most human of the Immortals, in his tones of grey and fallibility, and selfishness and selflessness, screwing up or just maybe doing things because he wants to, likes to, cannot resist the temptation of, while having unexpected flashes of generosity and self-sacrifice - yet we can never be 100% sure what his motivations are, deep down.
Well, or maybe we can just go with a cracky, but perfectly reasonable explanation and say that he's part human, part cat *grins*.