Here's my take on it last night
Winner
Harris owned it. She knifed Biden so smoothly in a way that he couldn't really counteract. She came across as more than qualified to be president. And she also came across as the one that could best take down Trump.
Buttigieg made a good impression. Mostly he showed that he deserved to be on the stage, which is a win. But his big moment was when he took direct responsibility for the police issues in South Bend and said flat out he wasn't able to fix it. I think that honesty will help him a lot.
No Change
Sanders is what was expected. He didn't improve his standing, but neither was it hurt.
Losers
Biden was by far the biggest loser. He went in to this as the clear leader and no problems or criticisms had hurt him. And then Swalwell brought up his age, with a smile but in a way that will have some impact. And the Harris hammered him. It's now clear that he's in the fight of his life for the nomination.
Yang & Williamson made it very clear they should never have been on the stage. Williamson at least had some interesting comments (wacky but interesting). Yang wasn't even there.
The other four – totally forgettable. All except Hick had one moment where they made a good contribution to the debate (Bennet's was another knife into Biden). But they're uninteresting and unremarkable next to Harris, Sanders, & Biden.
Hick: Props to Hick as he was honest about his views and his record. Some of that was phrasing ("Colorado" was the first to legalize marijuana leaving out his opposition), but he was honest.
Bennet: Bennet on the other hand gave a very false impression of himself as someone who fights for the people. What a crock.