Unfortunately, STO has some rather serious downsides, in my opinion. For one, the Klingon content is not merely negligible, it's insulting. There is -no- PVE content for the Klingons to speak of. No real story that you play through on their side either. Sector space, which is how you travel between planets is...tedious, but also something you can't just click and walk away from, lest you get pulled into a random encounter based on the auto-pilot. Further, the entire things is instanced. It is designed so that you will -never- under any circumstance have more than fifty people in a single instance. Sure, you can hear people talking in the other instances of the area you're in, but you can't actually get more than the max number in that instance at once. This, of course, also seriously destroys any value major hubs have as hang out points.
Speaking of the instances, there's another problem with them. Essentially, aside from the major hubs, you can't revisit areas. You get a mission, you go there, you complete it, it's gone. Last but not least is the problems with combat itself. It's...dull and repetitive, even for a MMO. Most of the time, the only strategy there is to the game is button spam. Hit 'em 'till shields drop, then hit 'em some more.
I won't deny, the story sounds interesting when I read it, but the execution is....severly lacking. Considering what they've done with the Klingons as a playable faction, I'm torn between the desire to have a MMO in which to be a Romulan and a desperate desire not to have them so underdeveloped and misutilized as the playable content for the Klingons currently is.
In short, it is my opinion that the game is probably a good bit of fun for nostalgia, thanks to continuity nods, but probably not for anyone that's looking for a MMO to occupy their time with for a while.
Stricly my two latinum on the subject, though.