As one of the guys who made the KKS remarks, I'll expand on them by saying that I appreciated my training because of the intensity. The moves were quite simplistic, but we trained the heck outta them and banged up our bodies pretty hard getting ready to use them. Pretty much every sparring night ended in some significant injury, and we were expected to show up the next workout, and just keep slamming away (broken left ankle? Lead with your right, and avoid weight-bearing while working on hands and counter-attacks [since springing into an offensive would be tactically and physically difficult in a cast]. Busted right hand? Rely more on your left, your legs and feet, and work on setting up right elbow instead of right punch. Etc.).
Every workout involved bag and makiwara work, as well as breaking (drop through a couple stacks of concrete or scrap-wood 2-4 nights a week, constantly challenging yourself to break more, and a puny little nose bone starts looking about as hard to break as a thin cracker). Each session also consisted of "tempering" exercises to condition the body to deliver hard blocks and blows causing injury to the other guy, and not yourself. Pictures of Mr. Oyama's knuckles were blown up and framed on the walls as the ideal to strive for.
I don't remember any of the forms, or if we even had any...I was usually in too much pain from a dozen sprain/strains and small fractures/dislocations, and just showing up and staying mentally present to get through class/conditioning took all the mental resources I had available (not to mention, I have a bad memory anyway...can't remember the names of kenpo techniques, and been doing it almost my whole life). I don't know enough abou Isshin to compare, but I wanted to be clear from the start about why I appreciated Kyokushin-Kai.
I also, ironically, don't recommend it for anyone not in the active military or law enforcement. I have a plateful of arthitis aches and pains, the vast majority of which are from this type of extremist training. Now, as a citizen without the need for this type of intense reaction capability, I have no justification to myself to use as solace for my aches and pains. It takes too long to get moving in the morning, and with no bad guys to chase or freedoms to defend, I spend that first 30 minutes pissed at myself for the folly of youth.
They may have developed a more family-friendly version; again, I wouldn't be in the know to comment.
Dave