They play terrible football. It's turgid, wretched stuff and makes you want to claw your eyes out.
Ferguson's style was also kick-and-rush footy built on diagonal passes or long balls to the winger/full-back then crosses (or set-pieces) into the box, but his teams did it with pace and it was more watchable (but not that much in recent years) and hard to play against.
When you watch City, Arsenal, Liverpool, Southampton or Everton... then watch United, the gap in the quality of football is enormous. The five teams play a modern game, United don't and won't until a). they get a manager with modern day ideas and b). the players to go with and less of one dimensional athletes like Jones, Young and Welbeck.
They have ruined Kagawa, a technically gifted player who flourished in Klopp's modern system/tactical style. Kagawa would be good at City, make no mistake about it.