It's not bad to compliment a woman's breasts
Just as long as that isn't all you compliment.
Unfortunately, if you just say "Wooo, you've got great tits!" that says to most women "I didn't get my eyes out of your cleavage long enough to notice the rest of you."
A woman who compliments a man's chest, or any other part of his anatomy has seldom spent an entire conversation addressing her comments to that part. Sadly, the same is often not true of men, particularly when the woman in question really does have great tits. (Note please, I say often, it's not a general judgement on the male of the species)
I used to work with a man, who I swear, after a year, couldn't have described anything about me, except the shape and size of my boobs, until the day I took off my jacket in his office and he was faced with a T-shirt that said "My face is that way", underneath an up arrow.
By all means, compliment our breasts, just as long as you realise, and let us know that you realise, that the rest of our body is more than a means to transport those breasts from place to place.