The large size of the reactions menu feels pretty odd to me. Perhaps they have been influenced by the large size of emoticons in apps like Katalk and Google Chat.
Still, my first impression is that it seems like an awkward in-between size: not conspicuous enough to fit in with the current scale and not large enough to set itself apart well.
I don't understand why they are so hideous. The colouring doesn't match Facebook's branding at all, the rounded pop-up box isn't used anywhere else, and the magnification stretches outside of it.
It looks atrocious. Like they didn't even care to make it look seamless—it's just a cobbled together add-on.
Or perhaps it speaks to a big UI-style refresh that they're going to roll out?
It definitely feels like they're moving towards a UI refresh just based on some of the tweaks they've rolled out lately. Besides, they're due for an overhaul.
Still, my first impression is that it seems like an awkward in-between size: not conspicuous enough to fit in with the current scale and not large enough to set itself apart well.