Without even reading the other responses, there are three, massive "unexpected" trades that happened.

1st up I'd have to go with Mitchell van der Heidjen to New England. From an outside-looking in perspective, and as someone new to the league, seeing the guy who scored the cup clinching OT goal getting traded the same day was a shock, and as far as I can tell the reaction from the league followed suit. Really, if every single person on the site knew MvdH was on the move after the finals, the context of him scoring the cup clinching goal and then getting traded is still insane.

Next up I got FR Finn-Rhys. I don't know if this is a surprise to everyone, as I'm privy to some backroom stuff with Edmonton and knew this move was upcoming, but contextually it should still be surprising. In 3 years Edmonton has lost to Hamilton in g7 twice, and was reverse swept before having another crack at them. Things were primed for them to continue to make things tight as the clear 2nd best in the west but they defied expectations by trading the recent Stevens winner for a haul of younger players. While many pundits continually predict Edmontont to get stomped by Hamilton, a lot of their ability to push through to game 7 has come down to their elite top pairing, and taking that away makes their performance this year less guaranteed. Plus, FR going to New England was surely a surprise... well actually it feels like New England is at the centre of all these big trades.

Finally we have the Alexander Oscarsson trade. Again, due to backroom stuff and DMing some friends on interested teams that tried to trade for Zema, I was aware this was coming, but contextually, another huge surprise. New England is on the up, they have a great young defense core headlined by Yxskaft, FR, and Oscarsson, but suddenly Oscarsson is on the block? SFP makes a buyer-ish move for a high potential, young D-man in a league that is always clamouring for young talent, so this move is a surprise to me and has the potential to really change the landscape of the league in the next few years.