There's no logical argument against MMOs in terms of entertainment hours vs money spent.
They're cheaper than pretty much everything that's not entirely free.
Another matter, though, is whether the "entertainment hours" are comparable to the ones you get with a singleplayer RPG.
That is an entirely subjective thing, and there's no way to make that determination in any other way.
They're promising 200 hours pr. character, and that's just the story content. If the game is anywhere near KotOR quality - I'd say that's a very nice return on your investment.
Now, I don't believe they can fully pull it off, and I don't believe that the MMO structure can truly match the sensation of being at the center of it all - without breaking all kinds of immersion barriers. Also, I don't believe that they can create cutscenes and emotional context on a "modern singleplayer level" - so I'm expecting something slightly quirky and more than occasionally unconvincing.
I also don't expect the level of closure I'd get from a singleplayer CRPG. If they intend to make this MMO last for years, which they obviously do, then they can't end the story with any kind of true finality. Seeing as how you're going to be able to go off the beaten linear path and complete all kinds of sidequests or "MMO stuff" - I don't expect to feel as if I'm finishing a game - but just one story.
Not sure that will accomplish for me what a singleplayer game normally accomplishes. I'm fairly sure it won't.
It's not the first MMO to focus on story - not by a long shot. LOTRO did it very well, but without voice acting. Age of Conan did it for the first 20 levels - and there are others.
None of those games truly pulled off the singleplayer sensation of getting a cohesive wholesome experience with the required amount of finality to it. They were too rooted in the traditional MMO conventions for the other parts of the game, and it remains to be seen if SWToR differs in that way.
But even if the actual story content is subpar and middling, I happen to quite like many MMO features - and I like the idea of being a part of a "living community" even if I'm not particularly social with strangers. I'm especially interested in how they're handling crafting and open world PvP. Both things have potential to be worthwhile activities.
Also, it's one of the VERY rare RPGs with several appealing classes. I'm not sure I've ever played one with that many that I wanted to check out. I'm expecting, at the very least, to play it through from both the Republic and Sith side - which means 400 hours of potentially strong singleplayer content.
It's basically 15$ for a month where the problem isn't the amount of content, but the limited time you have available. Even at 8 hours a day, you couldn't get through more than half of it.
Not a bad deal, is it.
The unwillingness to pay 15$ for that huge amount of content, is one of the major reasons the genre has been infested with F2P models. Nothing is more detrimental to gaming than that - and it has all but ruined the future of the genre.
I understand the trepidation about committing to a monthly subscription, but if you have any intention of actually playing the game - you're not being fleeced.