Man U only started showing good results at the end of the season... But failed to achieve anything other than a place in the Champions League next season... It's probably too early to talk about any success because Man U has always been a top club that has often played in European Cups... This season they haven't won a single trophy, although they have competed in many competitions... I think they have a lot of work to do...
I would say given the pit they were in last season, it's tremendous achievement for them to make into top 4 at least. They have gone through a lot over the years so they did well. Also you can't expect them to get hands on everything in just a season of rebuilding. It would take a bit more time before they really can be considered as a contender in competitions. This season they actually won EFL when they faced Newcastle in the finals and scored 2 goals.
I would however agree that they still need to work a lot and hopefully ten Haag will cover that in next season.
I am also not going to say too much trash about Manchester United. After all, they made a good comeback after all the problems they were facing. Generally achieving a Champions League position is not a very tremendous achievement for a club like Manchester United.
Considering the fact that they had been facing a lot of problems, I will say that they did well in the end. But I also agree that if they do not do better in the next season a lot of people will start questioning their performance.