Baka-Raptor’s reckoning that Kei was 20 times better than xxxHOLiC’s first season is somewhat hyperbolic but I do agree with the core of his argument. Watanuki is, or rather - becomes, less whiny and shows tremendous growth as a lead. But also because, as he changes, so do the people around him and their interactions.
The character of Kunogi Himawari stands out in this respect. I had thought that Itou Shizuka had been rather wasted in playing this supporting role since she had so little screentime. I had only read the manga up to Vol.9 so I was surprised and delighted by her arc across Ep 11 and 12 of Kei.