When iPhones first came out they were a dream to use - but I think that was largely because they didn't do very much. Picking up an iPhone 3GS (the first one I saw in real life) the interface was fast, intuitive and accessible.

However, as more features were added, Apple's desire to keep things appearing to be simple and clean, and their refusal to increase screen size, meant features get hidden away, behind swipes, long presses and double presses from different parts of the screen. I find iPhones really hard to use nowadays - even though they now have a lot of features which stopped me from buying them initially.