Its a mixed bag really. Our squad just isn't balanced at all, and I don't mean number of attackers vs number of defenders or things like that. The type of players that they are. Too many similar players who like to come deep to get the ball and pass it on right away, no incisiveness and cutting edge (for the most part, Di maria and Herrera the exception), nobody particularly fast or really strong (again Di maria and then fellaini the exceptions), a lot of just average physically players. Individually apart from Di maria, nobody takes players on and dribbles past them. You need that balance of players who can do that as well as have players like mata, Carrick, blind. We don't have a good mix of player styles pretty much.
Individual quality wise we are ok, and we could even put out a nicely balanced team, it would just require dropping a few big players and playing lesser players to balance us better.
Player wise, we have the best keeper in the league, but then the defence is inconsistent and injury prone at best. If they magically get past their injuries, then Rafael, Jones, smalling and Shaw could turn into an excellent defence IMO. That won't ever happen though.
In midfield, Carrick and blind are class as deeper lying playmakers and I want to see them together in a double pivot type formation. Then we have Herrera who provides a good different type of quality along with fellaini providing physicality and height. So not too many problems there, but a Strootman would be very helpful to be an all rounder type who is physically strong as well as a good passer and energetic.
Up front is where the most problems lie. Rooney, Falcao, RvP and Mata are all pretty slow, or at least, not fast or explosive. You want some pace to stretch teams as Van Gaal said, but you don't want to sacrifice Di maria who's our best player in his correct position and offers basically everything the rest of our squad lacks (pace, dribbling, incisiveness, great eye for a forward pass, that bitbof individualism, etc). Wilson is still too young and raw to really play a role, but you can see what he offers. RvP, Falcao, Rooney and mata really can't play together though, or at least it has to be Rooney behind Falcao or Mata behind Rooney, nothing else really. If I was in charge I'd let both RvP and Falcao go and bring in a more dynamic striker, one of these so called new agueros who have pace and are good on the ball and can really stretch teams with their ability, so we have rooney, new striker, Wilson and mata for the #9 and #10 roles so to speak.
So in summary, individual quality isn't the problem. Its having too many quality players of the same type and not enough different players like Di maria. For what its worth, I think our signings were really good for the most part. Blind provided that replacement for Carrick who is very versatile, Herrera provides an injection of pace, energy and creativity from deep, Di maria is that world class quality with real pace and ability to go past players and can create chances constantly, provided there are runners in behind. Shaw has obviously huge potential as a left back. Rojo still has a few quedtion marks if he's good enough, but he seems decent on the ball and good with the ball on the floor, question still out on him. Falcao the only pointless one of course, I doubt we'll keep him as he lacks that pace and physicality we need.