A lot of new fancy visual effects have been added to the game. Most bullets now have some visual effect and explosion on hit. New background elements are layered on top of the old ones to add more depth and randomness to the stage. Enemy spawns have been reduced but bigger enemies now have more health. Also added a bit of weapon tweaks. View the full patch notes in the link below.
Patch notes:
https://steamcommunity.com/app/1108250/discussions/0/1626286205698271098/