I for one can't agree with the hate on the second season. I know I'm definitely in the minority here but I actually preferred the second season over the first.
Why? Because in a shorter runtime I felt that season 2 did more for me as a story. Season 1's character development was very dragged out and took too long to take place, while the development of Suou from season 2 really showed her growth from beginning to end. Suou's progression from an average girl to a cold, jaded contractor to even learning the truth about her origins was really striking and took development a lot further in 12 episodes than anything in season 1 did. Season 1 was episodic and thus I had little real motivation to continue with it, while season 2 had a more compelling sense of urgency and intensity plotwise. Season 1 DID have more badass action, but I felt that season 2 proved that Hei was competent even without his contractor powers and that was something special in itself because many contractors in the series are utter garbage without their special abilities. And action alone doesn't carry a series, that's Bleach's main problem. Luckily DtB season 1 does have the sense of mystery and darker themes surrounding it so it's not quite like that, but at its core if you don't like season 1's action there's not really much to compel you to continue whereas season 2 didn't really rely on that.
But I will agree that season 2 is a drastic change from season 1. A word of warning to anybody who expects another DtB Season 1 in Ryuusei no Gemini: the atmosphere is very, very different. People who go into it expecting a picture-perfect replica of the original will probably hate how much it changes. Sadly, it always seems that people do this without even bothering to acknowledge the strong points of Gemini, which I feel are easily on the tier of the previous season if not even more so considering it only got half the time of season 1 to work with yet got nearly as much done overall.