I just finished SotC tonight. Wow. What an amazing game.
Technically, it is pretty flawed. The frame rate is down right AWFUL in some places (oddly the ending seemed to be the worst spot?), but it is great. As was mentioned above, I'm not sure a second playthrough would be nearly as exciting, but I love the idea. Just when I thought the game was getting repetetive and rather predictable, they kept throwing in new things to figure out. Very much fun!
Thanks for the suggestions guys! I'm not sure how long I'll have my PS2 (might opt to sell what I've got in light of new gear coming out this fall/winter), but this is by far, in my opinion, the highlight of the PS2. Truly a great experience, hampered only by the frame rate issues.