I'm also going to say that now having had a couple days to think about it, that I love this trade.
Tarasenko
-Tarasenko thinks shoot first which is something that has been missing from this team
-Tarasenko is constantly moving to create open passing lanes, in all zones. Hopefully putting him with Panarin will result in few turnovers for Panarin as Panarin's turnovers are frequently forced passes to teammates that aren't open. Therefore it stands to reason his turnovers will drop if he has a teammate open more often.
-Tarasenko being able to skate with the puck and handle should also create more space for Panarin.
-Tarasenko addresses one of our team's biggest weaknesses while allowing everyone else to slot down into their proper spot.
-We now have a legitimate first line that is ballpark with all of the other top lines in the league, and potentially does make us a legitimate Cup contender.
Mikkola
-Mikkola addresses the other of our team's biggest weaknesses (3rd pair LD).
-Mikkola is also a massive upgrade to Harpur...while not quite as big on paper, he's still very big, and very strong. St. Louis D has underperformed all year so I wouldn't be too concerned about his numbers resembling Nemeth, and instead focus on the body of his game. He'll put the puck to the net when it's warranted, and not when it's not (which is already an upgrade over Harpur), and is a lot stronger (and will take more penalties - as we saw last night though 2 of them were absolute BS) but is better in the corners and in front of the net, and is a way better skater than Harpur.
-Kakko now has a friend on the team, for those who feel from a chemistry standpoint this is important. Kakko's comments that he was happy are encouraging too. I think the impact of this is sometimes overstated, but I think when the mindset with the kids is "be yourself, play your game as you try and get better" a friend that allows the player to relax and converse in the home language can contribute to that mindset.
The Departing
-Blais did not add much. While his hitting was welcome, it did not often change the complexion of a game, he's not strong on the cycle or in possession or defensively, and his shot is not impressive. I still don't see the value in trading for him as part of the return to Buchnevich was what he "provided" even before the knee injury is something that can easily be gotten around the league. It's not his fault the trade was as bad as it was, or that Slewban destroyed his knee, but in many ways this is addition by subtraction. To those who say he was a friend to Laf and that's important for the reasons above I noted for Kakko, Laf still has Gauthier who speaks French...and the kid line as a whole has enjoyed good chemistry.
-Hunter Skinner was a fringe prospect at best, and won't really be missed. The odds that he's even as good as Mikkola someday are a stretch.
-The first round pick was a high cost in a good draft, but the Rangers still have the other one, and there is a good amount of young talent here already that needs time and space to grow into their fullest potential. Crowding the picture would probably have resulted in fewer opportunities for everyone. Based on the Rangers' system/values of player development, they should probably be drafting for upside five years out anyway, even in the first as even the best prospect won't be cast in a scoring role for quite some time given the players that are already here.
-Fourth round picks are not valuable commodities so I have no issues with trading this. The success of a 4th round pick depends more on scouting, knowing the player you are drafting's compete level, and blind luck, moreso than its position.
-The waiving of Hajek I didn't love only because him and Chytil were fairly close (see comments above about Lafreniere). Harpur is not a great player and to be honest either of them could've been waived to make room for Mikkola. Hajek is pretty bad, but in limited action, he's always played exactly the same even if he hasn't been in a game for months. With Harpur and his general lack of mobility, I'm curious how that plays out if Harpur draws into the lineup after a month+ if he will even be in game shape. I understand the move, but I just think that in reality Harpur and Hajek are interchangeable and either one could've been waived so why not Harpur.
Overall
Overall, I think this trade, if everyone can stay healthy - makes us a legitimate Cup contender for the first time since 2014-15.
I will refrain from commenting on the salary cap constraints for now because much of whether this move makes sense longer term will hinge on how much money the players try to get and the structure of their deals to commit to a team that - if it can somehow keep everyone except Goodrow (because there's going to have to be some cap casualty) - could stand as a serious Cup contender for at least the next 3 seasons as currently built. Obviously, no one knows what will be in the players' or their agents' hearts right now, so I'll leave that for another day.