I watched all of them. I liked Manizha's song before and now with the performance, I think it's going to be really powerful, lift you up in a way. Malta definitely interesting, good song, nice beat to it. Serbia seemed dancy, something I personally like. Not sure about the rest, France, Bulgaria, Switzerland getting a lot of talks but they were honestly kinda boring to me. I prefer fun songs so maybe that's just me.
Yes Serbia has a pretty good song IMO but I liked their colored 80's fashion dress in their video clip, and now for their live performance they seem to be dressed all in black while dancing in front of a dark background(with 10kg more 
). Where are the colors and the fun of their video? They want to look like opera singers now?France is the favorite of the bookmakers at the moment but it's highly overvalued IMO, moreover people don't like to spend money to vote for obvious favorites usually.
Yup, Serbia has such a cheerful and upbeat song, but it's rather forgettable, in my opinion. And yes, it looks like they gained at least 10kg each compared to the official music video.
I know it is not okay to comment on a woman's weight, but it's their choice to show so much skin, so...
Barbara's song "Voila" has that classic French flair (reminiscent of Edith Piaf's "Padam, Padam"). It was time for the French to send a decent song after a series (except for 2018) of bad songs and performances. After listening to all the songs, I felt she had potential (remember the Portuguese song from 2017? ), but I think that this year, considering the overall situation with the Coronavirus pandemic, we need something more optimistic, more cheerful.
For the Barbara's song I agree with you it's very similar to padam, too much maybe