I'm still playing through the late game, but a couple things come to mind:
My favorite boss fight, from late Act 2...
I absolutely loved the First Sinner fight - very fast paced but not too punishing, perfect for getting you into the flow state where you feel like you are just kicking ass.
And a moment from early Act 3 which I just went through today...
In the fight with the Bell Eater, when Bell Beast comes to your rescue... and then meeting the Bell Beast babies <3