The answer to "what makes Zestiria not good" will probably vary between people, but for me at least it was largely the convoluted equipment fusion and equipment skills system, and the story and characters are, while certainly not awful, nothing special either so.......
The battle camera kind of sucks too. I mean, you can often fix it, but the fact that it gets like that at all in a game in this day and age is kinda not good.
It not all bad though, as there were some things I liked, and it still plays enough like a Tales game. It's just that when you've been playing the series for years you kind of want more than just what's passable, especially when you know that they have the capability to do so (this is an issue I have with Pokemon as well).
MGS 3 with the Fox Engine sounds cool actually, but....pachinko machines? Really? That's what they decided to put it on?