If you buy a MMORPG, chances are that you expect a very different experience from what you would expect when buying a single-player game. As a result you'll often hear people saying that you can't compare MMORPGs to single-player games. But what if we throw this convention overboard? How would Star Wars: The Old Republic look if compared to a single-player game, how would it do as a hypothetical Knights of the Old Republic 3?
The big difference between single-player games and MMORPGs is obviously the number of players. It is possible to notice the existence of other players in SWTOR: In the first week of the game there were queues caused by other players, SWTOR has a certain amount of group content, and you might see other players killing "your" quest mobs at some occasions. But it is totally possible to play SWTOR as a single-player game: All the group content is optional, and if you see other players in game you can simply imagine them being NPCs with a weird AI.
So how good a value for money is Star Wars: The Old Republic when you actually were looking for a single-player game, for KOTOR 3? I would say it is holding up surprisingly well. You might niggle about the stories in SWTOR casting you slightly less as the savior of the universe than you would have expected from KOTOR 3, but otherwise the single-player experience comes very close to what you'd expect from a Bioware single-player RPG. There is a big main story quest, numerous side-quests, a typical Bioware mix of dialogue and combat. There is even a space combat mini-game thrown in for free. If you buy SWTOR, play one character to the level cap within 30 days, and then uninstall the game, you will have gotten good value for money compared to typical single-player games.
If you level a bit slower, or want to play through the game a second time, then of course SWTOR becomes more expensive than a single-player game. Nevertheless a second play-through is probably still good value for money if seen as a single-player game. You just need to choose a character from the other faction, and get a completely different main story line, and different side-quests as well. Even combat might be somewhat different if you chose a class that isn't the mirror image of your first character.
But while a second play-through might be better in SWTOR than in most single-player RPGs, replayability goes downhill from there. With your third and fourth character you will already have the same side-quests as your first or second character, and pretty much the same sequence of planets. Your fifth to eighth character can help but have the same abilities as your first 4 characters, or mirror images thereof. And after having played through 8 characters, you have probably seen every dialogue in the game. As cost per month remains the same, but your experience becomes less unique over time, at some point you'll probably think that it isn't worth it any more as a single-player game.
Personally I took a 3-month subscription for SWTOR, and I'm pretty confident to get value for money over the resulting 4 months in terms of single-player experience. But I will look long and hard at SWTOR at that point to decide whether I would want to play the game longer than that. Because in those 4 months I will not only have pretty much exhausted the existing single-player part of the game, but also the part of the multi-player experience I am actually interested in, that is playing through the small group content once. And then it's down to a rather typical long-term experience with a rather typical MMORPG: Repeatedly doing the same small group content, or repeating the same large group content every week, or doing repeatable quests, or doing PvP. Some people like that sort of repeating content, but I am not too excited about it. Let's do this again and see whether I can squeeze 3% better performance out of myself? I'd rather not! I don't give a damn about continuous improvement of my performance in video games. Especially not in the type of game where your improved performance only makes you better for this ONE encounter, and is of no use for the next one.
I can recommend Star Wars: The Old Republic as a single-player game. If you were waiting for KOTOR 3 and were unhappy that it might never be released, SWTOR is a viable alternative. If you don't mind paying twice the price for SWTOR than KOTOR 3 would have cost you, you can probably get 4 months of good single-player experience out of SWTOR. And that is it. Afterwards you would have to pay for a multi-player experience. Which might or might not be better than the multi-player experience other games are offering, but is probably rather similar. If you liked SWTOR as a single-player game because of the great story and dialogue, the multi-player experience will have far less of that; and it will play VERY differently from the single-player part, will presumably be a lot harder, and in any case be a lot more repetitive. You will need to see whether that is something that interests you.