Get in. The main issues that most seem to have about him can be easily argued really
1) Not giving youth a chance.
Only managed clubs where the priority was instant success, didn't really have the need for planning too far in the future. Anyway, Van Gaal has given more chances to young players then any manager ever would. Look how well he's done. If a player is good enough, they'll force their way through. The only thing that will stop is mediocre youth team players being given chances just because they're youth players.
2) Playing style.
He played great stuff at Real Madrid, and often times at Chelsea too. It's just in big games where he tends to be pragmatic and grind out results, but in the smaller games, his teams tend to get a good amount of goals always.
3) Attitude off the pitch
Just look at Sir Alex... There really isn't that big of a difference between the two of them in terms of how they were with the press, falling out with some players, things they said, etc.. For Mourinho's feud with Wenger, look at Fergie with Rafa or many others before that. Or Fergie refusing to do bbc interviews for so long. The list goes on.
Hopefully this gets sorted soon, as with him next season, you can be sure we'll challenge for everything. No doubt that he'll have his wish list prepared already for this summer in terms of ins and outs.
