Anyway, I'm a straight male, but I can usually appreciate the male form to a certain degree (I think women have the prettiest form by far but hey, I was programmed that way by my hormones). For the record, I think Hugh Jackman is the sexiest man on the planet. I find it interesting when you go back and look at the first actor to play james bond: a surprisingly undefined Sean Connery that wouldn't even be allowed to take his shirt off in a modern bond flick. Then you go back to the greeks and you get back to that ripped look. Although they always seemed to do sculptures where the males were, um, limp? Fortunate for us otherwise I suspect a lot more statues wouldn't have survived intact.
This brings me to the thing that bugs me about the male form (as others have mentioned): the genitalia. From a sexual standpoint and part of that male prowess thing I can understand the appeal when a man is, err, turned on (oh god this is barely going to be pg13). But otherwise it's just a veiny rod that doesn't follow any of the rest of the lines of the male form when erect and just a shriveled pickle the rest of the time. And that's before we even start talking about the balls... To be fair I'm actually grossed out by both genders' genitalia (and before you start with the smart remarks I'm a grown adult that has had sex), but the male one I actually find ugly from a purely aesthetic point of view.
Uh, so yeah. I get the male form from an aesthetic standpoint as far as the body goes (I always thought that muscular v line the torso gets is pretty cool), but the bait and tackle just ruin it for me. It's like taking a perfect sphere made of glass the sticking some mud on one side: it wrecks the view. This is why I typically prefer erotica over full hardcore pornography.
To put some contrast here, I like the female form for the soft curves and flowing lines, even on muscular women. I always liked the inferred texture differences between men and women: an idealized man is flat and firm, while an ideal woman is curvy and soft. It makes for fascinating art because there's a built in contrast whenever you put idealized forms of the genders side by side.