SO3 is definitely worth buying. Mixed bag it might be; but it's still a fun, lengthy game with a detailed storyline and plenty of little extras to keep you occupied. I still haven't finished it. The difficulty of the last boss is hideous, but at least it's a challenge.

Personally, I hated the plot twist. But the game's other merits made up for it. The characters are entertaining, there are multiple paths to take in terms of who joins your party, and the graphics are sublime. But there are quite a few people out there who don't like it, so my suggestion would be to rent it first, and see if it's your kind of game.