I could suggest tartarusnet for horror. You wouldn't have any castmates but there are other video game characters and people familiar with space adventures. It's a mostly slow paced game though people do tag at at medium paced speeds sometimes. The game itself involves being brought to the Greek Underworld and physically marked with a letter that represents sins that characters have committed during their lives. They're then tested and punished for those sins to see if maybe they'll change.

There are pretty active NPC's that characters can interact with. Characters can also influence the plot or NPC feelings sometimes. A while ago characters were able to influence one of the main NPC's into taking their side and helping them out more.

If you have questions I can answer. On another completely different note, I also play Samara if you'd ever like to musebox something!