1. Perhaps give it an upwards boost when it starts.
2. Perhaps make it continue until landing.
3. Perhaps make it continue in the air as long as the button is held down. (But also have a fixed minimum distance)
The reasoning behind one is I think it will look better visually. The reasoning behind two/three is sometimes it stops just short of an airborne enemy which then flies into you. It may not end up feeling good, but it's an idea to try if you wish.
I actually really like the air slide, regardless and that it moves faster than walking makes it a new movement choice.
Small thing:

A bigger thing.

The hitbox for the slide should probably be a bit larger. The enemy I'm mostly on top of isn't dead.
Some of the jumps and things are indeed tough now, since I guess they expect the old physics, but that's less work to change, probably.
Sorry if I was too rough.
Edit: Another thing I just noticed. There's a flash when you pause and switch weapons. (Probably related to how it removes the old weapon's object). The flash may be intentional, but I don't think I like it.