It's so crazy to see that an invite-only game is able to pull these insane player numbers.

I've even seen some of my friends, who haven't played since the start of the closed beta, come online again and try out the game.

Absolutely insane!

I'd attribute the huge spike more to the new beautiful map. The new characters are pretty awesome to mess with, though.

Definitely!
How are you enjoying the game so far?
I think Baba is currently a bit too much with her 80% spirit resistance to be honest.

It's good! I think there is still a lot of acclimation occurring within the gaming pool, especially when it comes to the new objectives like the poison pit and the bell tower, but my matches so far have been pretty close and overall pretty interesting.