What should we make of the most complicated transfer in the January window? Here are seven thoughts.

1. Sanchez is an instant upgrade for United

He's a better player than anyone at Old Trafford not named Paul Pogba or David De Gea. That much is clear. His style of play and the fact that he has been in England since 2014 suggest that he'll have an instant impact. Sanchez won't require massive tactical adjustments and isn't charged with central playmaking duties, either.

Sanchez just turned 29, and while his game relies on athleticism as well as technique, you'd still expect to get at least three good seasons beyond this one. Plus, this year, since Chile failed to qualify for the World Cup, he'll enjoy his first summer off since 2013 and should be fresh next season.

His arrival probably means Jose Mourinho will dispense with traditional wide men once and for all. That's fine too, despite what the old-timers who pine for old-school flying wingers at Old Trafford say.

Juan Mata, Marcus Rashford and Anthony Martial aren't traditional wingers, either. You'd expect one of the latter two to join Sanchez behind Romelu Lukaku in something like a 4-3-2-1, with broad licence to come inside and wreak havoc.

2. Sanchez's wages could unsettle other top United players

We don't know the numbers of the deal, but we've heard plenty of nonsense about the size of his paycheck -- half a million pounds a week, according to some unconfirmed reports -- his signing bonus and the lump-sum commission paid to his agent, Fernando Felicevich. Money does matter even to a club as profitable as United because ultimately it's about resource allocation. Pay a guy more than he's worth, and those funds can't then be used for another player. Simple as that.

One way to think about how much Sanchez is costing United: Take the money spent to acquire him (in this case, the bonuses and commissions paid), divide it by the length of his contract (4.5 years) and add his annual wage. My guess is we'll have a clearer picture as more details emerge.

If he's anywhere near the money quoted -- I haven't been able to confirm this, and I suspect it's substantially less -- it's going to be a big number. The good news is that a big chunk of it can be absorbed in United's wage bill by the fact that Mkhitaryan was a on a sizeable salary himself and Zlatan Ibrahimovic, the club's highest earner, will be off the wage bill when he's out of contract this summer.

The question is what impact this has when other United players come knocking for new deals. Both De Gea and Pogba can make a solid case that they ought to be the highest earners at the club, and both are way below Sanchez levels. In some ways, Sanchez's deal will cause the whole wage bill to rise -- one of the reasons City cited for abandoning their pursuit -- and you hope United are prepared for it.

3. Is Sanchez just another mercenary?

Had Sanchez opted for City, he would have been "reunited" with Pep Guardiola, keeping whatever "word" he might or might not have given the club in the summer, showing ambition to be part of one of the greatest sides ever, playing fantastic football and making history. Instead, by taking United's money, he's showing himself to be just another selfish mercenary.

That's one popular view floating around but it isn't as if Guardiola is Sanchez's personal guru. They spent one year together in Barcelona, where the player struggled mightily. He has already been part of one of the greatest sides ever.

And we ought to be grown up enough to know that committing to join City last August (when Arsenal eventually nixed the move) is different from saying "no" now. A lot of things happen in six months: Had he shattered his leg, would City (or United for that matter) still have been so keen on him?

That vision, peddled far and wide in some quarters, is as absurd as the other one that states he's going to Old Trafford because he was a United fan as a child and is capping a lifelong dream.

It is possible that Sanchez became a red while growing up in poverty next to the saltpeter mines of Tocopilla in northern Chile. Possible but unlikely. It's even more unlikely that after nearly 15 years as a professional and plenty of sacrifices, it suddenly became a decisive factor.

4. United will give Sanchez more opportunity to shine

There's an obvious parallel with the decision Sanchez faced in 2011, when he chose Guardiola's Barca over City, then managed by Roberto Mancini, who were offering more lucrative terms. This time he made the opposite choice, choosing the rebuilding club rather than the finished article.

There's a strong footballing argument here, too. City's game is far more schematic and far less extemporaneous than United's right now. Sanchez would need to fit into Guardiola's setup. That would mean either being an up-and-down winger in the mold of Leroy Sane and Raheem Sterling or, more likely, operating as a centre-forward, at which he'd be competing with Sergio Aguero and Gabriel Jesus.

At United, he'll have a more pragmatic coach in Mourinho. More importantly, the massive financial commitment the club are making suggests they will be hugely invested in him and make him one of the centerpieces of the side. He wasn't getting that at City. While in the summer there were suggestions that Aguero might be moving on at some point after seven years in Manchester, that looks less the case now.

5. Sanchez's agent played this brilliantly

Felicevich got himself a massive commission, he got his client an enormous salary and, perhaps most impressively, he got his client the option of choosing between two enormous, well-resourced clubs. You really couldn't ask for more, could you?

Then you have Mino Raiola. By sending his player to Arsenal, Raiola will allow Mkhitaryan to hit the reset button at another big Premier League club and with an improved contract. Raiola will be able to go back and have leverage to get a better deal for his clients at Old Trafford, Lukaku and Pogba. Not too shabby.

6. Is this good business for Arsenal?

The move is great for Arsenal because they lose Alexis but get Mkhitaryan, a gifted player who is roughly the same age. One Arsenal fan I know made the point: "In this market, to get a player of Mkhitaryan's quality, we would have had to spend £70 million. Instead, it's just Alexis, who would have gone for £35 million now or zero in the summer [when he's out of contract]."

Those are some pretty Gunner-tinted glasses through which to view this. Although plenty has been written about the increase in transfer fees, if somebody out there really were willing to pay £70 million for a 29-year-old Mkhitaryan, you'd imagine United would have sold the Armenian international to them.

Is it better to have Mkhitaryan than £35 million in cash? Maybe, though when you consider that it's unlikely his agent would have him take a pay cut, he'll still be the highest-paid player at Arsenal. In fact, what he'll earn isn't far off from what Sanchez would have cost if they had extended his deal 18 months ago.

More importantly, getting the best out of a bad situation now doesn't erase the mistakes Arsenal made before. Like turning down the £60 million City were offering in the summer for a player with an expiring contract or letting his contract run down in the first place.

7. Mkhitaryan is the obvious winner

He's still at a huge club on the biggest domestic stage, he's still earning a bundle and he'll be, you'd imagine, central to Arsenal's plans. It's another shot at being a superstar in England with a club heavily invested in you, probably more so than the previous one.

Now it's up to Mkhitaryan to seize the opportunity. Whether he succeeds personally or not will depend on other factors as well, such as how Arsene Wenger views him and -- it's Groundhog Day -- how long Wenger sticks around.

But with a director of football who has worked with him before in place (former Borussia Dortmund scout Sven Mislintat), a big wage commitment and Mesut Ozil on his way out, you'd imagine Arsenal are willing to build their future in the final third around him.