Here's how I would view United's transfer window:
Romero is not good enough. He's already cost you points that De Gea would have saved against Swansea and it says something that he was available as a free agent. I don't think De Gea still being at the club is anything to shout about - he'll be in no mood to play and is bound to be angry at United (justly or not) that a deal couldn't be pushed through. Plus, Van Gaal is far too stubborn to start picking him now. The same goes for Valdes, who Van Gaal has also fallen out with. With the sale of Lindegaard, that realistically leaves you with Johnstone backing up Romero. Nowhere near top class.
The farcical nature of the De Gea transfer reflects badly on both United and Real.
Darmian is a good player and a definite upgrade on Rafael. I can't believe you haven't signed a top class CB. You thought you were getting Hummels at the start of the window, then Ramos as part of a De Gea deal and then interest in Otamendi. After all that you're left with a pairing of Smalling and Blind with Rojo seemingly also falling out with Van Gaal and Jones injured. Shaw has been OK since the start of the season. Massive questions about depth though - you'll have to play a lot more games this season than last and are already resorting to Blind (a DM) at CB. I don't think you've got any bespoke backups at full back with players like Smalling, Jones, Valencia and Blind having to move out of their comfortable positions to provide cover.
The best improvements are here. With Schneiderlin, Carrick, Schweinsteiger, Blind and possibly Herrera you have a group of fairly solid players. I do think Schweinsteiger is a little bit past it though (he's given away possession a lot so far) and he might be on too high a wage to not play regularly.
Depay could turn out to be a good signing but he's hardly set thee league alight so far and was definitely a gamble coming from the far inferior Dutch league. Mata's decent but IMO you have to put Herrera in the hole behind the striker or you really lack creativity. Again, maybe lacking depth after letting Januzaj go.
Rooney's off the pace and you've decided to support him with a completely untested 19 year old who's immediately under enormous pressure due to the incredible fee paid for him and that you also have no depth here either (unless you really want to count Fellaini). Selling Hernandez and Van Persie (and losing Falcao) without bringing in a senior striker is very daft IMO. Martial has only completed 6 games in his entire career and 8 of his 9 goals last season were against teams in the bottom half of a much worse league than the PL. He is the biggest gamble I can remember ever seeing a club take on a player.
In short, I don't think you've really improved this summer since the effective loss of De Gea will cost you more points than the unproven attacking players you've brought in are likely to add. You've lost an awful lot of depth as well with more games on your calendar since you're back in the CL. You may well get in the top 4 again but I find it incredible that that's the aim after the amount of money Van Gaal has spent making the team his. I find it even more incredible, the easy ride the media are giving you for apparently having no title credentials despite the money spent. When City had spent a similar amount we were being derided for not winning the Champions League, yet alone competing for domestic honours.