I thought the tactics in the first game were fine and I agree with your take on why we didn't win. I also don't think we won because of the different approach, I'm just explaining why I think he decided to try a slightly different tack.
To be honest, he could have sent probably have sent out 10 men in a 2-2-5 formation and we'd still have won but I don't really think the team he did select is worth getting worked up about. The Rooney in midfield thing has been going on all season and most of us hate it. It's obviously here to stay for this season, though. Whether that's because he really doesn't rate Rooney as a striker or thinks he brings something to midfield that the alternatives lack we might never know. But it's clearly a response to a squad of players that isn't where he wants it to be. So it seems reasonable to stop crucifying him for it unless it continues after this summer.
The other decisions in formation and tactics last night were really no big deal. A bit of squad rotation (which is essential to give game time to fringe players - in a season when we're playing so few games) and using Fellaini in an advanced midfield role to unsettle a defence and keeper that dealt very comfortably with the high ball the last time we played them.
I just think you're inclined to be very negative about Van Gaal so are looking for reasons to complain. I sympathise with your stance, as I've had my own reservations all season. You have to remember that we've endured weird team selection, tactics and formations with Fergie plenty of times before though. Usually during transitional seasons (remember when the fans used to chant "attack! attack! attack!" or the Alan Smith and Rio Ferdinand as CM experiments?) We've also endured some really dull football, in the very recent past under Fergie. So I do think you're exaggerating about this season being the worst football you've watched in 40 years. We've had plenty of ups and downs but the downs were always ignored (by you and me anyway) because we had 100% faith in the manager to turn things round. It seems unfair to be constantly on Van Gaal's case, when he's probably just going through the same difficult period Fergie often went through when he had a squad that was missing the last few pieces in his jigsaw. I think we have to be patient and forgive the occasional eccentricity. Last night was an utterly dominant performance that got us the result we needed. Seems churlish to use it as yet another excuse to criticise IMO.