Well, indeed Mr. Yoshino doesn't seem devoid of talent at all, but this is also why I get particularly annoyed when he umm... does shit. But then again Mai-HiME had an enormous cast that was managed well, and that is no easy feat. (Look at Nanoha StrikerS, an anime of the same length and a established background already for contrast) For an extreme example, see DBZ, where the author can't even remember some characters.
In a way, he's actually similar to the infamous Mari Okada. They both write significantly worse male characters. I'll let Shu off the hook, but come on... Tate... there's no defending this guy.
Ironically, the Mai Otome manga, of what he is the author, would make Okada
extremely jealous.
However, when kept under checks or provided with a source, they seem to do fine. I notice they both seem to be best at writing attractive, strong women. (Mai-HiME was chock full of these.) Surely, he can't get credit for creating Snow Black from Accel World, but given the base of a character, and she simply rocked. It fell straight in with his talents. I should watch Macross Frontier.
On the other hand, when either of them go wild, you get some really really silly things, to say the least.
Both of them worked on Fractale. Does anyone remember that?
But yea, in my opinion they certainly have had better times (Mai Hime, True Tears). Note that Mai HiME wasn't as big of a sales hit, compared to Otome. Shall I rephrase? In their current state, it's pretty much the opposite of what I want.
I also have to agree with Kaioshin somewhat on NisiOisin. The witty banter is amusing at times, but I think the overindulgence and clouds of smug tend to dampen any sort of cleverness that pops out. He's generally the opposite of the above. He writes good male characters, but his female characters, well... umm they're sort of the opposite of what I consider good ones and some come off as too much of a sexual fantasy and not enough depth, rather just objects of desirability. >.> And this is coming from someone who loves Kuroneko from Oreimo, and she is a basically a nerd's fantasy.