The iPod was more than an MP3 player improvement. It was huge (in terms of storage space), personal, portable, storage for your music. Everything out there at the time held far less music or was far bigger and it was making an assumption that people would drop cash to have all their music with them pretty much all the time. The iPod was super ambitious and it was more than just an improvement unless you just want to call everything an improvement in that there was something like it beforehand. But then you get into saying something like well the iPod is really just an improvement on the sony walkman tape player because it served largely the same function.
But even you have to admit the iPhone was really revolutionary. It was true internet in your pocket made simple enough that the masses could use it nearly instantly. In case you don't remember, there was a time when you simply had an iPhone and the internet with you at all times or you didn't. The other smartphones that folks carried (largely blackberries) couldn't do anything on the internet with any speed that was beyond excruciating. The internet was the iPhone's killer app and it was available from day one.
Finally the iPad took the iPhone and said the realities of human scale means the phone size is too small for many tasks. Let's make it bigger even though we are asking people to carry what in someways is a duplicative device was the genius move. Getting a screen that large, having the battery last, making it affordable and super profitable was Apple's supply chain at its best.
All game changers in my mind.
This is a draft of an digital audio player (properly named DAP) that was filed for a patent application in 1981, which predates the (overwhelmingly overrated) holy grail iPod by about TWENTY YEARS.
Then of course there were a boatload of other viable mp3 player options even before the iPod, and even more during the early 2000's some of which were far superior to iPods (check iAudio aka Cowon). To this day, since the existence of Cowon, iPods have been inferior, but like the stereotype goes, its true that people go for the brand/logo rather than the functionality. Apple's yet to release an iPod with real EQ settings, battery that lasts more than 40 hours, open source video codec support, a removable battery, decent sound quality (ipods have always scored worst) and my personal favourite; being forced/locked down to iTunes to transfer your own media to the device but not being allowed to take it back without the use of 3rd party applications.
As for almost all of Apple's products, theyve all been evolutionary. When you look past the media hype and the brainwashing thats been done from Steve Jobs' reality distortion field, theyve never really 'revolutionized' anything; they took GUI, the mouse and networking from Xerox, their mp3 player was just a rehashing of the old, almost none of their product's components are their own, the iPhone is simply an easy to use but reliable phone (nothing more).
But I'll give Apple credit where its due;
They really know how to make user interfaces.... DAMN WELL. Their products aesthetic design is amazing. Their software and advertising of their products is as reliable as they claim it to be (unlike Microsoft).
And OS X....
This is what bugs me most. Of all the platforms that Apple's been selling, OS X has been the slowest to take off. People went crazy over iPods. Theyre obsessed with iPhones. And now the insane loyalty and behaviour for the company has been furthered by the iPad (a product which I see as most useless in Apple's lineup).
But the BEST product Apple has had, OS X, nobody even bothers to say 'Yeah, I really like OS X over Windows' but rather you hear people saying 'I want <insert iOS product here> or a MacBook' without acknowleding the fact that OS X is the reason why Apple's *real* computers have been so good.