1. The amount of content that is out for wow.
Websites with vast databases
Guides
Addons
Past experiences
We didn't have crazy addons which pointed where to go. Questhelper wasn't a thing.
we didn't have wowhead.
We had thottbot which might have had a few comments or a general idea of where something was. Or we asked in general chat.
We were clueless..
2. We already know what will be needed.
Resistance, spawn location of different things, Nature resists and frost resist gear in future 1.xx patches. We know that we need dwarfs or undead for healers and tanks.
3. We don't play with the same people.
There won't be nostalgia feeling.