That ipod still works. Every once in a while I charge it and listen to the gentle clicking of its tiny drive.
I think the first Windows compatible iPod was the game changer. It had a large HDD but was much lighter and smaller than similar HDD-mp3 players at the time (such as the ones above).
Part fashion accessory, part music appliance, part computer, the purpose of the iPod was understood by Apple and poorly understood by their competitors.
Just like how the Walkman wasn't the first portable cassette player, or even technically the best, Sony relentlessly innovated on that form factor making smaller, lighter versions, waterproof ones, and ultimately owned that market. It wasn't until the iPod rolled around that someone displaced that position so completely.
I recall it being very difficult to explain to my peers what I was carrying. Thankfully the nomad looked like a CD player.
Sure, at that time, few people had a Mac, but certain demographics had it. And I distinctly recall that people in the office were curious about the iPod, and were impressed with the intuitive UI (with the physical scroll wheel, which was really quite nice - it had inertia and would spin a while when you spun fast).
FireWire, integration, and storage size ("all your music in your pocket") definitely played a role. Basically, if you had an iTunes library, the iPod was a total no-brainer.
(Off topic, but not that much: my sister grabbed her first iPod as a windows user approximately 12 hours after the 3G became available on the shelves here in Italy, mainly because she had been so envious of mine... so anecdotally there was quite a lot of pent-up demand, and they were smart to bottle it up to the point of explosion and then harness it.)
I mean, I had a iPod, but I used 3rd party software to load it since iTunes was mess.
My recollection of the time was that most MP3 players were based on Flash storage rather than HDDs, so I could get about 10 songs onto mine.
Macs didn't really take off as a thing until long after iPods had been mainstream for a while, so I don't think the integration was actually very important compared to the fact that there was a well known HDD-based MP3 player.