Although I take issue with the question being explicitly addressed only to people who actively use feeds, because many groups.io users may not fall into that category, it is a good question.
What I like is being able to specify what is and what is not of interest to me. I don't want, for example, every activity by every FB friend shoved in my face in that feed.
In the groups.io feed, as it currently exists (although I would not, strictly speaking, call it a "feed," as mentioned before), there is absolutely no consideration given to user preference. Every group I'm in is included, some of which I have more interest in than others. That forces a lot of scrolling on me. Maybe I don't want an extremely active group in which I have the least amount of interest, which is more active than the others just because it has 5,000 members (or other reasons), to constantly appear at the top and force me to scroll through all its activity each and every time. Maybe I don't want some of my groups included at all.
Maybe I never use chats and have zero interest in them, no matter which group they're occurring in. Or new files. And yet, there again, currently I am forced to scroll through chats (and files) of every single group to get to the info that is actually of interest to me.
Instead of scrolling through pages of what to me is a bunch of junk, I avoid the feed page altogether and am glad, due to the insistence of some of us, that there is now a clickless way to do that. Making the feed the landing page for everyone was a big problem.
If groups.io could allow users to customize their feed by stating their preferences, even with a simple yes/no checkbox for each group and each kind of activity, that would make the feed something that I might actually use instead of having to manuever around.
Messages are the sole opinion of the author, especially the fishy ones.