Here's my problem with Fourze, in a nutshell: There were so many things done right, but SO many more that weren't, and most of all, I think the pacing just sucked.
By the way, the Gemini arc was one that, whilst I enjoyed, I thought could have been built up right form the beginning. Yuuki got more manic as time went on, right? But not progressively so. At least, not really. It was more unpredictable and just all over the place, with no rhyme or reason - as if she was just having constant mood swings every episode or something (which wouldn't be surprising, but you get the idea). If they had built her up much more progressively, where she was getting cheekier and more reckless with each episode, then once the Gemini arc finally came up, *bam*, hell is unleashed. I also think the Gemini arc could have been placed earlier in the series, but then again, half the series felt pointless, and only a few of the Horoscopes have any real character building (Scorpio, Cancer, arguably Libra and Sagittarius, POSSIBLY Aries and Leo).
Oh, and Aquarius? That arc just annoyed me. Something about that girl just drove me nuts. People said she was a good actor who could portray lots of emotion. I think my problem was she portrayed TOO MUCH emotion.