Top 4 Teams in last year's CL in terms of possession were: Barca > Bayern > Real > Juventus. Notice a trend? Dortmund were the go to team for fast paced direct football for quite a while, their squad is still almost the same that was build around that style. Guess how much possession they average this season: 58% - 3% more than United. [Squawka]
If you want to be successful over a long period you need to be able to control games and have the tools to keep up circulation in dangerous areas, at least that's what the past few seasons seem to sugggest.
Bayern and Barcelona, two of the top three teams in the Europe right now, play football rather similar to van Gaal. You might argue that he laid the foundation for Bayern's style during his time there.
The huge difference in contrast to United's previous style is precisely the reason why people should be more patient towards van Gaal. He's laying the foundation of a true European top team again, by teaching the players how to control a game. Penetration comes next, but you have to take one step after the other.
No they don´t. Just because all these teams use dominance by possession does not make them similar in style. That is like saying every counter attacking side was similar to Klopp´s Dortmund, which is just as untrue. There are vital differences to the systems of Bayern, Barcelona or Dortmund.
This starts with the focus of the systems. If I would have to describe United´s current theme in one word it would be "composure": composure on the ball and in terms of organisation. It is hard to catch them on the counter or disorganized. The whole setup is very stable, which can be seen the most in the midfield. Van Gaal clearly prefers a pair of more defensivily minded central midfielder, basically playing with two anchor players, which helps their back line a lot and irons it out. It works very well to isolate the opposing striker. This is a stark difference to the other mentioned teams, who all play with one defensive minded player in front of the defense line, who is supposed to stabilize and balance the formation. This frees up an additional player for the more advanced (in terms of positioning) creative role in the center. Guardiola even "sacrifices" a defender from time to time to get a number advantage in that area.
Like United every possession orientated team faces the main challenge of cracking heavy deep lying defenses. These parked buses are not created only out of a feeling of inferiority in terms of playing strength but are also a direct result of the system. If one setup is supposed to get as much time as possible on the ball, the other will normally not chase the ball around all the time, but rather sit deep, limit the space in the final third as much as possible and hope for a chance on the counter.
Each of the mentioned teams use different tools to break these defenses:
Barcelona has still a huge focus on passing strength, especially accuracy. They circulate the ball nearly perfectly, while waiting for an opportunity to get the ball to their front three, who are all extremely strong dribblers, who either score by themselves or bind defenders to create space for the other two.
Bayern has also a high emphasis on passing, but their even bigger focus lies on positioning. The reason why Guardiola is so pendantic about that, is that it makes them the strongest team when it comes to playing between the opposing lines. They use their fast wingers, who function more like inward forwards and cut into the box from the side, to wreak havoc there, they have with Müller an extremely intelligent player who is a pain to defend and has a rather unique eye for space and with Lewandowski arguably the strongest striker in the world when it comes to shielding the ball and playing with the back towards the goal.
Dortmund´s answer is a very offensive use of the fullbacks. This is in itself not that different to United with Darmian and Shaw, but they use it to intentionally overload one wing to stretch the opposing defense and disrupt their organisation. Once that is accomplished there are multiple ways to create chances: a cross or through pass to Aubameyang inside the box, who is very good in finding goal scoring positions very quickly, hoping for Kagawa to use his strength in crowded places to slip through the cracks, a lay up to the edge of the box where the extremely strong shooters Reus and Mkhitaryan wait or a simple flank change to the other fullback, who is now mostly unguarded and can send the ball right into the center of the box with a single touch.
Now, what are United´s options? Well, there are not many. The problem lies in the above mentioned system. While it is very stable, organized and gives a lot of control, it is also a double edged sword because it is very rigid. This makes it rather predictable and thus easier to defend. It puts an even higher emphasis on the indiviual skill of the offensive players, because they often face tougher situations as result of the opposing defense managing to prepare better.
To put it simply, United right now appears to be a team which is hard to beat, but has at the same time a hard time scoring goals / winning without massive effort. An higher emphasis on set pieces could help them to score the crucial 1:0, which naturally draws the opposing team out of their really defensive states (worked wonders for Dortmund in 2013/2014, who also had a hard time vs. very defensive opponents). That or they could hope for one of the offensive players really hitting top form and managing to score by flashes of brilliance (see Martial´s goal or Depay´s perfomance vs. Brügge). Given the rather short list of players with a big goal threat, the chances for that happening are not the best, though.