I think the answers are contradictory because the experience is different for different people. Not all men are alike, and not all women are alike.
For me personally, it's sort of hard to describe. I'm not into drugs, but I'm guessing it's like being on some sort of powerful euphoric drug. Being with the person you're in love with is like a shot of adrenaline. You feel more energetic and just more alive. Your heart can literally start pounding as soon as you see her. When you're not with her,
you can't stop thinking about her. And not just sexual thoughts--you may fantasize just about things you'd like to say to her or places you'd like to go with her. If there's some day when you just get to see her for five minutes, that will still be the high point of your day.
Everything in the whole world seems more vivid and more real. You almost have to resort to metaphors here. It's like impossibly good music is playing just for you. It's like you're walking barefoot in the grass on a bright spring day after endless months of dreary gray winter. It's like you've recovered from a long sickness and now you feel like running a marathon. Sorry if I'm getting a little poetic here, but I'm not sure how else to put it!
If there's a difference between men and women, I think it's that men tend (on average) to have, well, somewhat wider standards for who they find sexually attractive. So you may meet tons and tons of people that you find attractive that way; which means there has to be an extra-special something-or-other to really make you fall in love. Once you do, though, there will be a sexual component to it. The person you're in love with will become extra, extra-attractive.
Another difference is that I think men will be more likely to become very protective of whoever they're in love with. There's a negative side of that...being protective can slide into being controlling. If you know what you're doing, you'll keep an eye on yourself to make sure that doesn't happen.
Then, of course, if things don't work out it can be crushingly depressing. It's like you have withdrawal symptoms from the drug. The whole world will seem empty. You can go for months having a hard time concentrating on your work or daily activities. Hopefully, you'll recover after a while.
Maybe the word "you" is wrong here--really this is all "me." As I said at the top, I'm sure plenty of men do have different experiences. But I hope this helps some!
(By the way, I wouldn't say I've ever had "butterflies in my stomach." Actually, I'm not quite sure what that means...)