I'm just going to assume that some Nike intern accidentally switched United's and Arsenal socks for the manequin display, since United doesn't wear red socks and Arsenal doesn't wear black socks...
If the sock situation gets sorted out, I think both United and Arsenal have very nice looking uniforms for next season. Ours sort of looks like pajamas and I think they'll get a lot of backlash for that, but I really like that Nike is going for something different. I really like Arsenal's design also.
Unfortunately, my first impression of that Barca kit is... Ugh. Gradients almost always look really really bad. To be fair, though, when I first saw the design for the Catalans' current home kit I wasn't impressed either, and now I love them. So we'll see.