Hmmm...Interesting discussion you guys are having.
I personally don't like MDWAV III because it was too confusing, the costumes were lame, half the main cast missing, and there wasn't enough SL X TY interaction. But mainly, I don't like it because a lot of the actors, aside from the main cast, didn't make me feel any compassion for them. They and their stories didn't make me want to get to know them or feel for them. A lot of them just made me really annoyed because they were taking all of the screen time away from Joey, Eric, Keneath, Pinky, Berg, & Cheung Kwok-Kuen (Fok Sung). At least in MDWAV I & II, I really liked all of the supporting actors, even the evil ones, and cried a few times for them when they had to make the difficult choices in their lives. But with MDWAV III, I was just really really annoyed.
As for Tian You and Siu Ling's love story.
I agree with you guys. There should be a MDWAV IV so that they can clear up the confusion to which Tian You Siu Ling really loves. Although, I would feel kind of bad for the grandson when he comes back since his grandpa has practically taken his identity and married the woman that he loved. So if his grandson came back, the person he loves would be his step-grandma. Awkward!