Well, I exchanged it at GameStop. Of course, it works fine, and I was able to get past the point it would freeze at, and I played up to Chapter 6. Unfortunately, after taking it out of the PS2, I noticed a light "ring" on the data side of the disc, not as hazy as the other one, and it's still reading the data okay. I tested another, cheaper, game disc (Jak II), and after five minutes, I took it out and noticed a one-line scratch ring. So, it looks like my PS2 has decided to start scratching the discs I put in it. Right now I have it disconnected, since it may be too dangerous to put another disc in it, and I'm trying to figure out what to do. Best case scenario: The lens just need some cleaning. Next: Try one of the fixes I've read about (Adjusting the lens, replacing the sponge thing, tape?) Worst Case scenario: I'll need to buy a new PS2.
EDIT: Found the scratcher. It wasn't the lens. Apparently, when the lens moved to a certain position, brown/gold wire that connected it to the motherboard arched so that it was in a position that put it in the drive bay itself. This "exposed" wire was too high, and would manage to to touch the spinning disk, causing the scratch(es). Right now, I'm moving the lens manually while gently patting the cable down, perhaps some adhesive might be necessary, but I doubt it.