I got my first iphone in Oct of last year (the 4s) and I have to say, I dont know how I ever lived without it. I was very resistant to buy an apple product for years, but I've officially joined the cult. I've heard some people complain about the battery life, but my iphone will generally go up to 3 days without charging depending on how much I use it. I love the mp3 player in it, I love siri that I can just ask the iphone a question and it will give me the answer without having to type that stuff in. For instance...if I want dominos pizza, I just ask "where is dominos pizza" and it will show me the closest dominos....if I dont care what type of pizza, I just ask "where is the nearest pizza place" and it will show me a list of nearby places and even has user rankings for how good the place is. I love the GPS and how I never have to buy another map or ask for directions again.
People say the camera is good, but I cant comment on that because I have a canon eos 7d DLSR camera which makes most cameras look like crap, but if I'm being honest, I have to say the camera is ok as long as there is lots of light. If you are indoors, it doesnt seem to take pictures as well.
The other thing about the iphone is the "coolness" factor. I dont consider myself a snob, but when I see someone with a smartphone that is not an iphone, I see them as someone that couldnt afford a "real" smartphone, or as ghetto phones. Once you get an iphone, you will know what I mean.
Think of it this way... Getting an iphone is like being on facebook. Getting a samsung galaxy or HTC is like being on google+
Getting a blackberry is like being on myspace.
100 million people have bought iphones...if it werent a great product, they would not sell so many.