Very customizable (I like having number row always visible, and having long press for symbols on each letter).
Has gif support built in.
My biggest pain point is:
It auto corrects words that are spelled correctly to other words. I type "our" and it changes to "out", I recently typed "purpose" and it changed it to "purple". Autocorrect is awesome and necessary, but I hate that it corrects words to other words and not just typos. I wish I could find a keyboard that has the things I like without this annoyance.
I don't use the gif keyboard or autocomplete, so I comment about that. but it's so much more customizable than gboard. Honestly surprised you found gboard to be customizable because in my experience it's one of the least customizable ones out there.