When reading a book full of action scenes, what do you want from those scenes in order to keep reading the book. What should a good action scene has and why should you keep reading it?
I like when an action scene is kept somewhat simple. If there is to much going on it can be easy for a reader to lose focus or keep everything strait.
I'm the kind of person that likes really tense action scenes. I want to feel like I'm a part of the action, that I'm actually there. I'm not sure if tension would be considered action in terms of what you're saying, but I know for a fact that a scene with either quick, snippy dialogue alongside tight environment descriptions keeps me going. Action (to me) is fast, so I want to feel myself reading quicker as I progress in the scene because I'm mentally a part of the action itself.
I want to feel like I'm watching people move and fight within a real space. Or perhaps a better way to put it is that I don't want to feel like I'm watching a really old Japanese role-playing game, where characters stand in place and take turns swinging their weapons at each other. I want a 3D environment with which the characters interact (cover, footing, etc.), weapons with heft and recoil, and injuries that actually hurt.
If you have decided to put your characters into mortal harm, show them being threatened by dramatic situations, or are showing them resorting to physical force to solve a problem, then I want to see the extreme limit of their traits and quirks. I want to see them pushed to their physical and mental limits, I want to see them sacrifice, and I want to see them act on their morals in a dramatic, exaggerated way. There needs to be a reason for the action. I don't want to see jabs. I want to see uppercuts. The black pawn has moved on the white pawn. I want to see blood and zealous morals. I want to see your characters' beliefs enforced or changed due to this drama I am reading. Something needs to come from this action. Otherwise, it is just worthless movement.
Something realistic and something that keeps you glued to the book so much that you actually read over words because you want to get to the good parts. Basically you're hooked into what the author is conveying.
This can be a major impediment if you're using a loosely defined magic system where anything can happen. I think wizards in those sorts of settings are better suited to manipulation and grand reworking than straight-up fights.
A good action scene should include emotional clashing, psychological games, and determination to prevail over immediate opposing force(s). I personally like humor thrown in, normally in mid-fall, mid-tumble, or when reaching for a device/weapon/item. The petite grandma or blind grandfather who projects a light-hearted tone is always fun. (Honestly, for some reason I am thinking of the grandmother's humor in Mulan, and the grandfather's in Charlie and the Chocolate Factory). Their temperment at points is priceless, worth more than a golden ticket, or a lucky bug. Shanghai Noon, Rush Hour, Indiana Jones trilogy, Gone Fishin', And Then There Were None... These have funny chase/action scenes, except "And Then." It is just an intriguing ending, more psychologically thrilling than active. Bruce Willis does masterful job of this in his early movies. Note: I am pointing to the movie scenes, even though the question is about books.