Aardwolf was fun, though I remember my big gripe was that it had a bunch of weird little themed zones like the Star Trek and Wizard of Oz ones that felt a little hokey to have in there. These days it wins solely by virtue of being one of the few that's still populated and free.
When I tried to go back to the Simultronics ones (Gemstone IV and Dragon Realms), not only was it a ghost town, which made random interactions almost stressful because you feel like two people walking past each other in a ghost town, but they have double, triple, and quadrupled down on squeezing their whales for every cent. A lot of people playing that game are paying $50-100 a month or more, and even normal players have to cough up more than the base $15 a month subscription if they want more than 1 character (!!!). Looks like their website has been stripped of all its cool character too. Shame.
These games in their heyday were truly a one of a kind experience. All of the weird online socializing you see people getting on platforms like Discord, but all wrapped up around a fun RPG game that felt so much more flexible and imaginative than other online games at the time.