My reaction to the twist was pretty much the opposite of everyone here. I had started reading YU+ME when it was still at part one, but I stopped reading it soon after discovering it because it was just another highschool-romance comic. The writing was okay at that point, the art was okay, although there were quite a few anatomy errors and I didn't much like the pacing; I found it unlikely that Fiona, an outcast for pretty much all of her highschool life, managed to make two friends within such a short space of time, and I felt as if their friendship wasn't properly developed. The story's focus really is on Fiona; there doesn't seem to be any character development until nearer the end of part 1, so I was REALLY surprised when it turned out Fiona like Lia in that way, because it really didn't seem as if she would.
HOWEVER. Some time later, I came across YU+ME again (I forget where - either an article or a webcomic posting). Seeing how much the art had improved (I'm a sucker for good art in webcomics), I skimmed through part 1 again and came to the twist. And I was really excited about it! I was hooked from that point on, and the coming chapters only increased my enthusiasm. The writing is natural, interesting, well thought out and funny, the art is absolutely fantastic, each style is unique and the pacing is much, MUCH better. I found this part much more interesting, exciting and better crafted than I ever found the first part. I would love to see the first part revised a little, to give Lia, Jake and even Don some more personality, although I can only imagine how huge a task that would be.
Anyway, I love the comic, and the twist was awesome. I can't wait to see how this thing wraps up!