It probably won't be outright essential, but it does seem to follow on directly from the cartoon and includes the same characters. You probably should watch it.
If you want to watch rebels at some point then watch that first because this series will definitely spoil a lot of the ending. Otherwise I guess it's just a bunch of characters you don't know the history of yet.
Oh no, there are many things not included here that’ll be a big surprise. Assuming the leaks are correct, that is. Not going to spoil anything here but there’s a lot not shown.
A bunch of cameos from other animated movies. The bearded "we no Jedi, mister" guy dies and therefore his whole existence is already pointless. Thrawn thrawning his way to his ultimate fate.
Eh, the trailer should feature 30% of what it showed and it'd be better.