Reactions so far from my experience are very limited (especially if anyone can jump to disengage removing attacks of opportunity). I hate to throw out that "other D&D game", but I have to say that having an option to cast feather fall on my recently shoved paladin before he goes splat on the rocks below is awesome.
One specific suggestion I have is to add a reaction to the surface area attacks that are so prevalent. Let me use a reaction to try to move out of the area before taking damage.
