Alright, I gotta come out and say a few things against the popular "Mourihno is negative" narrative. First of all, I am his fan. That's another story, but I wanted to disclose this upfront.
He is a defensive minded manager; I won't argue that point. But when he has the players with the right mentality and the right qualities, his style can be very entertaining. I found his Inter's side run to the treble very entertaining because of how well organized and lethal they were on counters, and also because that team was so united behind him as the manager. The way I see it, counterattacks are one of the most entertaining aspects of the game. The third goal against Arsenal was a fantastic goal; how fast they went from winning the ball to scoring, with excellent quick interplay between Lingard and Lukaku to get the move going.
When I look at the players that United has, I think that the team is a few pieces away from being incredibly successful playing Mourihno way. Martial, Rashford, Lukaku, Pogba, Lingard, all have speed and can punish teams with counterattacks. The missing pieces are a #10 with an eye for assists (Miki is ok, but is inconsistent and loses the ball too much), a left fullback that can contribute on the attack, and an athletic defensive mid (Fellaini is actually not bad, but it wouldn't hurt to have another option). What is also very important is that it seems that the young players that could be the core for the years to come (Lukaku, Pogba, Rashford, Lingard, Martial) all seem to be friends and enjoy playing together. I believe that if given time, Mourihno can build a formidable team.
To be quite honest, I find the United fans to be spoiled and overly pessimistic. Every loss, every bad performance, it's a tragedy for some reason. It's easy to be a fan when you're winning all the time. This is when you need to be a true fan. And it's not like there is no progress over the last season and a half - top 16 of CL (and probably more), currently second in the league (and even though chances are slim, there is still hope) - and all of this with a ton of injuries and suspensions. So you lost to City, but it was without Pogba, Fellaini, Bailey, Matic playing injured, Rojo injured at half time, etc.