The comments already made pretty well tell the story. The scent of a guy's semen is unique, not exactly like that of anything else, but bleach is the item its scent is usually compared to. I never made that connection on my own, when I was first becoming familiar with it, and if I'd been asked for a description I probably would've just said it's got its own scent, an odd one -- but when I first heard the bleach comparison I realized there was a similarity all right. "Musky" is another term I've heard or seen used. The consistency of the fluid is sometimes said to be starch-like, and I believe a scent comparison's made there, too.
The bleach smell is the chemical reaction of the sugar fructose freshly mixed with the alkaline elements of semen. The sugar is used to feed the sperm because they are small and don't carry much energy with them. The more sugar you have in your ejaculate the more bleach smell you tend to have.
From a lady's point of view, (we have had it in our vaginas, on our sheets, on our bodies and in our mouths - we know semen very well. lol)
I have found that all semen that I have had contact with smell and taste a lot like bleach.
I agree with Meg28. It does have a bleachy odor. All men I have been with have had an odor that can be compared to bleach, except one guy, and I hated the smell of his semen. He drank coffee nonstop and I think that had something to do with it. Bleachy is definitely "normal."