Well, as people say, it's pretty much a lightsaber version of WoW. SWTOR has amazingly good storylines for each jobs (in my opinion), while WoW.. well, does not. The thing people tend to complain about with SWTOR is pretty much the pvp system and the lack of content. According to my xfire account, I've played 222 hours of it since I bought it a month ago.
And about your question, yes it's monthly. Though with buying it, you get a month of free play time. Just so you know, many people anticipate that it will become free to play, so if you want to try it, but don't want to pay a monthly fee, yo