Agreed. Also, compared to using a good held item, I find them generally not all that helpful.
Well, they do provide the eye candy factor!
But yeah, I'm really disappointed how uncreative they were with Z-moves. Even the starter ones don't retain their unique properties when you use the Z versions (Operetta doesn't stay a sound move for example). Maybe they can come back and do something more interesting with them, but I think I'd prefer them add more Mega Evolutions personally, I find those are fun to play around with even if it ends up being a dud like Audino.
I get the need for Fairy typing to balance out Dragon, but it was a poorly thought-out concept in X/Y and remains poorly thought out. I also feel that Dark typing has gotten overly nerfed. Pokemon doesn't need any more new typings, but the current ones need to be rebalanced.
Ultimately a Pokemon's stats and moveset is usually a lot more key to their usefulness. Touch the weaknesses and strengths and the tier lists shift around a bit, and you can't really please everyone. I do agree some types need some help though, especially Ice defensively (but they actually referenced this in-game in XY which implies Ice being frail is totally intentional).
In terms of game balance, Fairy's kinda broken, yeah. They put the two most rare attacking types as their weaknesses (Poison and Steel), probably hoping it would make those types more popular because they are mainly defensive. It was actually somewhat successful, but I think they need to make another type weak to Poison as an indirect nerf to Fairy (I nominate Water personally). Fairy also shouldn't be resisting Bug because Bug was already terrible. The rest of it seems fine though IMO.
I think Dark types are doing okay personally. Dark type is actually one of the most useful types in the metagame, and a big reason is Knock Off, which not only a very powerful utility move but basically functions as a 100 BP attack with 100 accuracy. This gen also saw them gain an immunity to Prankster.