I've been playing Subnautica: Below Zero the last few days and it's good. I'd recommend starting with the first Subnautica though because the second one isn't finished yet, unless you like seeing how games progress as they're being made. I'm playing it now so I can compare it before and after the planned story revamp.
For playing with people, Warframe is a lot of fun, and they're always adding new content. I haven't played it since the Fortuna update though.