The St. Louis Blues get center Ryan O'Reilly.
The Buffalo Sabres get a 2019 first-round pick, a 2021 second-round pick, winger Tage Thompson, forward Patrik Berglund and center Vlad Sobotka.

St. Louis Blues: A-minus
There's something I like to call "NHL Trade Initial Shock Syndrome." If you'd like to know the symptoms of this condition, look no further than your first reaction to this trade. You saw five assets being swapped for one player, which is a ratio usually reserved for elite players such as a rookie year Eric Lindros. Ryan O'Reilly is not a rookie year Eric Lindros. You likely guffawed.
But take a step back, and consider the context from the Blues' perspective. They were thirsty for a No. 1 or 2 center after trading Paul Stastny last season and not being invited to "The Bachelor" rose ceremony for John Tavares. O'Reilly was one of the only players in the NHL who fit the description and was available, having professed that he lost his smile with the Sabres last season.
So they made the deal. But what did they give up?
Berglund is a 30-year-old good soldier and is signed through 2022 for $3.85 million. Sobotka is a 30-year-old depth center signed for the next two years at $3.5 million. The first-round pick will be in the bottom 20 based on the past several seasons (last year excepted) and is top-10 protected. The second-round pick is whatever. Thompson is a legit prospect on the wing, but here's what he isn't: Winger Klim Kostin, center Robert Thomas, defenseman Vince Dunn, forward Jordan Kyrou or goalie Ville Husso, all of whom would have been the kind of blue-chippers the Blues didn't want to par with.
Is it a haul? Sure. "But in a cap system, sometimes you have to do things that are uncomfortable," Blues GM Doug Armstrong said.
In O'Reilly, the Blues now have that essential three-deep depth at center with O'Reilly, Brayden Schenn and free-agent signing Tyler Bozak, with O'Reilly likely playing with Vladimir Tarasenko. The Blues got the best player in the trade and didn't give up anything essential to get him.
Oh, and according to Cap Friendly, they saved $775,000 in cap space for this season by sending three players back to Buffalo, which is a neat trick.

Buffalo Sabres: B
It's clear that GM Jason Botterill wanted to move O'Reilly before the Sabres had to pay his $7.5 million bonus money, and so the haul for him was going to be affected by that deadline. It could have netted them one of the Blues' blue-chippers, or it would have saddled them with O'Reilly until the trade deadline. "Once you pay that bonus, you're going to play that player until at least the middle of the season," Armstrong said.
That established, the Sabres add a few good assets to their lineup for a player who declared that he had basically lost his passion for hockey after last season with Buffalo. Berglund and Sobotka could both end up on their third line. The draft picks either will fill the coffer or can be flipped for other assets. If Thompson becomes something palpable, this might get bumped up to a B-plus.
As of now, they got a bunch of decent-to-promising assets for a player it became clear they had to move, based on his own comments, and didn't make out financially in the process from a cap perspective, even if they did in real dollars.