Anyone familiar with original D&D or any of its more recent clones will naturally know the gist of the system from the start, there are a few surprises within this tome however. It uses an ascending AC system that is a little different than usual. Proficiencies offer a grab bag of skill and feat like abilities that don't weight the game down (plus they are optional). There is a hard cap on character level at 14. Demi-human classes may have a lower cap, but it is less of a handicap when its only a handful of levels at most. High level play is VERY much meant to be about lords and their domains, of which every class has its own unique take.
If I were to ask for more out of ACKS it would be that it included an example domain to get you playing as soon as possible. That and maybe a little dungeon module.
All in all, if you enjoy OSR style gaming there isn't any reason not to give ACKS a look over for ten bucks. If you like enjoy it, the pdf has a coupon for those ten bucks off of the hard back if you just have to have it in good old dead tree. I'm definitely considering it myself.
[5 of 5 Stars!]