There are several starter designs past Gen III that I never really cared for. In Gen 4 I tend to just dump my starter.
I've started to dislike Zacian. It basically ruined the Pokemon Unite moba game, which was for a brief period actually sorta balanced and not-pay-to-win (except occasionally an overpowered mon for like, two days before it got patched). Zacian ruined all of that. Even after it became available to freebie players, it stayed horribly broken. Admittedly it can be very satisfying to gang up and murder Zacian, but if it gets any kind of lead it will just absolutely delete your team. Likewise I don't like the eevee-evolutions as much as I used to as the developers over-favor them and kinda spammed them. My understanding is that she (Zacian) is broken in whatever meta she enters, so this isn't unique to Pokemon Unite which is tbh a shit game that could be fun if the devs weren't jerks.
On the plus side, the game did make me like Greedent, Zeroara, Eldegloss, Cramorant, and appreciate Mr. Mime who has a really interesting play-style and has saved my ass a few times. Thank you Mr. Mike.
I don't really like most megas. I will ditto hating rotom.