While there are things I wish they would have done a bit differently, overall that was a satisfying end to the series. They managed to sufficiently get rid of the Jedi to keep the movies intact, explain where the heck everyone else was, and they did Thrawn justice by having him defeated without being the fool (as so many Imperials were).
The flip side is that an "and the adventure continues" is kind of annoying in that it's non-definitive; the characters all had proper arcs, but they don't all have proper conclusions. So now we've got 2 quasi-Jedis and a Mando artist running around the universe as what's presumably a hook for a future series. It's a bit of an open cliffhanger, and those rarely end well.
Overall season 4 was fantastic, to the point that I don't feel there's a single bad episode in the whole run. Which is all the more impressive considering the relatively modest budget compared to The Clone Wars and its pet-project funding. Which goes to show that you don't need a massive budget if you have good writers and a showrunner with a strong vision.
I do wish they had managed to find their feet a bit sooner though. A strong season 1 is unrealistic, but if they had picked up like this in season 2, I believe the show would have ended up more popular than it was.
(And Rex is Nik Sant. No one is going to convince me otherwise!)