1: Changed age rating (aka: Adult Swim). Suddenly it didn't have to appeal to children anymore, and that meant mature themes - like murder, suicide, romance, and nudity. All things that fans of the original show didn't want.
2: Ashi. She added NOTHING to the story, but took away a whole lot because Genndy wanted time to set up a romance subplot. Which, again, didn't add to the story and that fans didn't want to begin with.
3: Lack of imagination in general. It felt a lot more like it was just going through the numbers with what this kind of show is supposed to do, rather than doing it's own thing. Biggest example: to clear his mind of anger, he meditated, where he went to an imaginary dimension where he did a thing you see in kung-fu films that teaches patience. Once he accomplished this task, he realised he did not need to be angry, and so stopped being angry.>>96976888
Japanese waifuism is different. There, it works, because the attention is on making the woman interesting rather than trying to build up a romance - which they often don't even do. Ashi was plain ol' western romance hamfisted in: focusing on how the characters are luvvy duvvy with each other and not on the character being someone YOU'D want to date.