My experience is that of a 99% faction dominated server, so Timeless Isle was both incredible and highly toxic. Players had nowhere to hide. So all the while they're exploring this mysterious island discovering its nooks and crannies, meanwhile a war is being waged throughout between PvPers/Griefers and Carebear PvErs.
As the first Fire Watcher on the server, it was maybe the most fun I've ever had in the game. The battles, the rivalries, all the trolling and shenanigans. There were no lengths I wouldn't go to get my next Bloody Coin.
It was also novel in that it had tons of jumping puzzles and secrets. It boasted timed events, dailies, achievements, tons of vanity items and super useful items for the non-instanced world, 4 rotating world bosses with a secret area for legendary cloak wielders with another world boss, mounts, pets, the Celestial Tournament which was the first of its kind, and more.
Plus this was the most complete and fleshed out classes have ever been ability-wise -- before the Great Prune in WoD destroyed them -- so just the fact that classes were enjoyable and had vast tool kits made everything else about the game more fun as well.
I've got endless stories about my Firewatcher journey, what a time that was.