Ai reminds me a bit more of Yayoi than she does of Haruka nor Yukiho (though I can see why she gets compared to the latter two). I like Ryo's voice, but... yeah, Ryo bothers me a little. I don't know whether or not it's the otokonoko aesthetic or what. If they do bring Ryo back as more than a cameo I sincerely hope he got thrown a bone and could shed it, but the fact is that his being otokonoko is what makes him popular...
I'm not too fond of the mobile games in general because of the high amount of characters with minimal effort, and the high amount of unfitting fanservice. I, too, do not mind fanservice (like Metal said, it's an idol series and thus fanservice is going to occur), but when you have characters like Fuuka who specifically doesn't LIKE "sexy" work yet the producer (that is, you) tend to get it for her? I can think of other roles her character could do that aren't "sexy" - so it seems like a shoehorn. Yeah, Azusa plays the "sexy" type, but she's also played up in-universe as more than just that, and whether or not she likes/hates/doesn't notice or care about the fact she's fanservice isn't the primary point of her character.
Ultimately, every character is fanservice in some form or another. Given that the game initially had you focused on one idol and one idol only in its origins (from my understanding; I've never played the arcade or X-Box versions) it makes sense to provide different sorts of characters that people would like to deal with, whether it's the haughty Iori, hyperactive Yayoi or shrinking violet Yukiho. Ultimately, each of the original girls began as fitting a stereotype, then given elaboration, becoming fuller-featured characters.
It's whether or not they can be more than their stereotype, and how much it's emphasized, which worries me more. I don't think I'd have minded the introduction of new idols in the franchise, but they could've gone about it much differently than they did. There's definitely character types and roles they could have brought in and elaborated on that originated in the mobile games, and despite their lack of realism, they could've been just as good as the main core given some polish and effort - many, though, I agree can't be redeemed. (*stares Mayu down, not caring about whether or not she'd get killed*)
I don't mind the change in artist as much as some of you might, but I do see where the older artwork has its own appeal. But then, I generally prefer (most of) the 2nd Vision designs over the 1st Vision ones...
