DS9 is great! My favorite show by a good margin.
I've always had a bit of a mixed experience with Star Trek Online since I started playing it. It's fun, but the online portion of it tends to put me off after a while. I still end up starting it up a couple of times a year though!
Yes, there's an enormous amount of content there!
In most cases I don't like having other people in games either. It's very immersion breaking to have random people running and jumping off of things and who knows what else! Then you inevitably run into the person that just wants to ruin everyone else's day too.