it has 2 entirely new quests marine and pekora
that each have their own unique gameplay and stages to play through
plus an extra mode to play as noel only through flare quest.
there's a button to switch characters instantly now in flare quest instead of having to pause to switch every time now.
you don't lose your charge when getting hit anymore.
various stage differences to existing stages such as the mini boss in falls for flare quest is completely different now among other things.
balance changes for weapons and bosses etc. overall they're a lot of changes and new content that makes it worth buying.