It really depends on what level you are at, which style you do and what you're looking for. Keep in mind, I only have first-hand knowledge of a small part of ISKA.
As far as I'm aware ISKA cover quite a broad category of tournaments that fit under the Kickboxing umbrella. My experience of ISKA is in what i would call the 'Freestyle Karate' ruleset (it might be called something else, and obviously, no offence to any Karate practitioners out there) - there are two types of fighting - point and continuous - and fighters can usually choose to do either or both on the day. I've been involved in this at the Open level where basically anyone from any club that registers can compete and you are then split into categories based on experience and weight.
Point - fight until a clean hit is scored and then reset
Continuous - medium contact, keep fighting until the round is over or someone falls over/you get seperated. Resets are much less frequent.
Personally, I'm not a fan of the Freestyle Karate rules in ISKA - no kicking below the waist, no elbows, no knees, no grabbing legs or clinching and usually light(ish) contact. It can result in a lot of hopping around on one foot, as people use the rules to their advantage; great if you have fantastic technique and flexibility, but somewhat unrealistic and to be honest, it's a real pain in the *** if you're at a reach disadvantage and not flexible as hell.
Depending on who you are up against it can be a lot of fun though; my old club were quite well represented in my category so I got three fights that day with training buddies and we just went 'balls to the wall' with each other, which is really in the spirit of how we trained at the club.
My old instructors used to fight within these rules at European and World level but I can't comment on that.
At a high amatuer level, expect stuff like this: