Pretty boring. THey just popped some environemt, mobs, rares, treasure chests. Most people who loved it were super casuals who just liked killing stuff, and pvp griefers who loved the idea of messing with people. it had a good amount of various toys and alt-catchup gear, which justified going there for me.
Other than that it had no story, no explanation why all of it is there. Celestials had their training grounds right next to Ordos..... why didn't they deal with him? Tanaan was far better with story, purpose and different activities. Even the Maw was better despite not being able to mount. I like story-driven zones, even if they're as bad as the Broken Shore, Argus and Korthia.
Another major problem with Timeless Isle - it never stopped you. There were no goals apart from the ones you set for yourself, no limits. So it facilitated mindless non-stop grinding for the currency. And because of that, the prices for the items were pretty high, again forcing you to do the mindless grind if you wanted something.