I can only speak for myself, but the reasons I dislike the update:
1. It's missing small mode for absolutely no reason, since small mode actually still works perfectly fine with a workaround and should be trivial to maintain.
2. New game page is full of clutter I don't care about, I don't care about people getting cards, I don't care about other people's achievements (which btw are often spoilers), I ESPECIALLY don't care about developers streaming the game. I don't use social media, I don't want steam forcing this garbage pseudo social media on me. I might be able to accept the loss of small mode if I could remove all the clutter I don't like off this page, but you can't customize it at all it's just forced on you.
3. "What's new" tray is insulting. you can remove everything else from the page but not what's new. There is absolutely no excuse for this, I can't think of a single consumer friendly reason to make it unremoveable - it's blatantly there as an ad to sell you DLC or whatever.
4. game list on the left, then a giant cluttered mess of game box art on the right is pointlessly redundant. Why can't I have all text, or all game box art? Why do I have to have both at the same time? It's just such a wtf waste of space.
TL;DR all I want from steam is a list of games I can click on to play, they used to have an option for that and now they don't.