For something completely different, I play Dungeons & Dragons Online. I've been playing since it started 11 years ago and playing the pen & paper version for almost 40 years. It has FTP parts as well as premium parts that you can purchase. It captures the essence of the D&D world with changes necessary to make it playable online. The imagery is incredible. And while adventures are really designed to be played with six players, they have added hirelings (AI controlled characters) to assist. The hirelings do okay for what they are and make solo adventuring a little more feasible. There is a lot you can do without making any purchases, but eventually you will want to spend money on adventures that are not available to the FTP group.
It's not for everyone, but it might be worth a try. I'm on the Sarlona server if you're interested.