What makes the iPhone so good?

I'll admit, I am an Android chap, for now anyway. I've used it for as long as I can remember, and I love it. However, I've recently been getting more and more interested in giving iOS a go, perhaps an iPhone and iPad. I'm not sure that I should, but I can't imagine that such popular products would be worth anything less than what they provide.

And so, I'm here. I would appreciate it if some of you could list your favourite things about the iPhone, things that just keep you using it.