I haven't played the games, so I can only judge from what I've heard and from the two episodes of the anime I have seen.
I don't like Clemont's (Citron is what he was called in the episode I saw?) clothes, haha. He should wear something else :p But I guess there might be a story to it or something. Probably more clear in the games, and whenever Ash realizes that he actually is a gym leader. Otherwise, I think Citron seems like a pretty okay if maybe a bit dull character. They could have given him a nosier or know-it-all attitude instead of a general good guy.
Eureka is adorable! I hope they'll try to give her some cool adventures, like they did with Max. Hopefully some that will try to develop her knowledge and will to become a trainer, rather than just having her as the little cute childish girl. EDIT: okay Clemont and Bonnie are their English names. I got it!
Serena, I have hardly seen anything from yet. But what I've seen, I like! She seems a bit like a more May-ish Misty. Hopefully not as easy-going as Dawn but rather a bit more like a mix of Bianca and Barry, actually! That would be fun.
And Froakie is amazing. No arguing. :3 And MegaBlaziken, aaaah.