Not sure what Moirae is on about, there's practically no active PVP in STO. Everything is PVE based, matter of fact once you get your top level ship and gear fleshed out in your ship. You might start with joining in on some of the crazy DPS races for the raids and active events. There's tons of content and story arc's in the game that makes it worthwhile.
Ironically I'm not even a star trek fan, so I actually ended up learning a lot of the background lore from the game. It had me a peeled for a good year about 2-3 years back when I was in a gaming lull. I haven't been active in it for over a year now so I can't comment on population but I do keep up with the updates. I know they added a lot of more stuff now thanks to the new show.
Overall, MMO wise I'd give it a solid 7/10, it'll scratch your space itch that you're seeking for at least a little while. It's actually a game where you find out really quickly whether you will like it or not, none of that "wait til cap!" crap. Although I will say the ground combat and story lines are a little more interesting mid to upper levels.