It's strange. I have a hard time remembering why I liked Ubuntu right away. Maybe a blend of good enough looking, works out of the box mindset, which made a community grow rapidly and kicking a nice network effect where you would quickly find solution on their board/wikis.
I was impressed later when they managed to bring new Window Management ideas without too much time or pain.
It's strange. I have a hard time remembering why I liked Ubuntu right away. ... works out of the box mindset
Ubuntu was literally the first Linux distro I have ever used where everything on my PC worked out of the box.
Installing Windows (of that age, XP) on the same PC would result in spending a day or weekend hunting and installing drivers for obscure things here and there, but in Ubuntu everything just worked.
I had never seen anything like that before (on PCs at least), and that made a solid impression which still makes it my default, despite a interest and curiosity trying in other distros like Elementary or NixOS.
I believe Knoppix was the first to formalize the debian live cd concept—I don't think they did the major work for supporting hardware and supporting installation from the live cd.
I seem to remember they put a lot of early effort into getting almost all laptop wifi interfaces working out of the box, which was a massive deal at the time.
Warty Warthog happened to match my ideal environment out-of-the-box. With Fedora, Suse I'd have to to install my preferred apps, configure Gnome the way I like, with Warty it was all already there. Also it had modern kernel with lots of stuff in it. For me specifically it was SATA support and PPTP encryption stuff.
I was impressed later when they managed to bring new Window Management ideas without too much time or pain.