To be fair, I think he didn't get the chance to prove his qualities. Even if our defence was shaky at times, the opponents didn't get too many scoring oportunites. And the goals that Kepa conceded were mostly impossible to avoid. I think he was a bit at fault against Arsenal, but cannot think of anything other than that.
Regarding the game against Liverpool, I don't think he could've saved that shot, yet I would like to point out the good job that he did with closing Salah's angle in the first half, when Rudiger got that goal line clearance. Kepa's contribution was essential, as he made it very difficult for the Egyptian to get a powerful and precise shot.
He's a good keeper and I am sure he will get even better as time passes.