It's been difficult for me to imagine what being Flowey could possibly be like. My best guess is that he's been reduced to something like a pure observer, unable to attach special meaning to anything he sees because he has no soul to generate the emotional (rather than intellectual) responses to things that are the basis for our sense of meaning. After a while, I imagine, this must have sheer Hell to Flowey, all these monsters and their doings and his memories of them all, inundating him with information that he had no tools to sort. And everything he did just gave him worse and worse memories to add to the load.