We learned very little in the Book of Boba Fett that we did not already know. Four episodes of worthless exposition and flashbacks only served to prove that the series started at Episode 5, where we saw The Mandalorian's story start to progress again. By the end of Episode 7 the Boba subplot is covered and we're able to move on with Mandalorian stuff.
There was a lot of stunt casting and a lot of CGI bullshittery in this side-quest. We learned that some stunt casting, ala Danny Trejo, can be excellent but the best character development came from new characters ala David Pasquesi's nameless 'Majordomo.' Cad Bane gets the award for best fan service, by far.
Cad Bane was as Cad Bane as I could have hoped an old Cad Bane could be. I take issue with a chump like Boba ever getting the best of him, but holy smokes — the guy stared down a rampaging rancor. Bane sounded, looked, and acted like Cad Bane — down to his lightning-quick dodges and dead shot accuracy.
Luke also proved himself to be a CGI asshole, and Grogu certainly shows him up like a chump too. Seems pretty obvious that Luke should be sulking on a rock waiting for someone to eff up his 'saga.'
However, the only character developments we really care about are that Mando gets a new ship, Grogu gets some cool new threads, clearly has figured out the Force and Peli Motto is the new Star Wars sex symbol. All of these are Mandalorian season 3 stepping stones. The entire Boba Fett arc was nothing but a brief pause on our way to Mando taking the dark saber and doing some Mando stuff, that is the way and as Cad Bane said, now is where Boba jets off to his bacta tank.
It was nice to finally see Fennic Shand kill everyone she wanted to.