Yes Disc 4 was boring, (or for the xbox owners, the forest bit) but then again if you listen to all the conversations you find some nice bits of info that help you understand more of the game and of the characters.The fourth disc added a bit of variation, collecting bits of branch from a cave using your zippo lighter as a torch, anyone? Also Disc 4 was relaxing from the fast paced 3rd disc in Kowloon.
I think its a bit harsh to say the fourth disc destroyed the game, I still think Shenmue 2 is a kick arse game even if the ending was a bit dry.

P.S The tree outside shenhua's house, its called a shenmue tree, right? Or was I dreaming that bit...(Bit rusty you see, havn't played the fourth disc in a long time...2002 i think..)