Biggest changes since October, eh?

I'd go with the new producer / director Naoki "Yoshi-P" Yoshida as the biggest.

But in the game itself, probably a vast reduction in lag would be the first thing you notice.

There have been a lot of subtle (but mostly good) streamlines in the UI. Things involving repairs are a good example (totally changed for the better). Still room for improvement, but getting there.

The way you gain SP in combat has changed (works like XP now).

I'd say those were the biggest things.