A lot of Quality of Life improvements (such as weapon no longer trespassing walls, objectives being listed during the level intro sequence, better interaction with tutorial prompts, better playground stage, more accurate weapon handling, etc...), plus new features and levels.
Eight new levels based on old ones that will make you play them in a totally different way.
New objectives to complete, like earning points while freefalling from the sky, cleaning up a virus or completing a platforming puzzle.
Also new is a weapon that will be high-risk high reward, it gives a lot of damage but at the cost of being easy to miss and potentially losing the combo. You can use the weapon's ability for better results as it lets you remote control the projectile.
With this update, the Free Aim mode no longer is a cheat, so it can be accessed in the options menu and played without any of the penalties of using cheats.