DKC2 is a great example of a game that's for kids yet manages to be entertaining for all ages. It's a very simple setup, rescue Donkey Kong and the game play is, on the surface, very basic with most of the game just being a case of running and jumping on things. However the reason it appeals to such as wide audience is because it's challenging. It's easy enough at the start to draw in the less experienced players and have them work towards the end goals and get better but for the more experienced players there's tons of secrets in the early stages to find and some brutally hard stages in the games latter areas.
It's the same with a lot of games that are considered all time greats. Mario, Sonic, Donkey Kong, Spyro, Crash Bandicoot and all these kind of games have mass appeal because they are easy enough for anyone to understand but have enough going on for advanced players to sink their teeth into.
It's basically how Nintendo have acquired most of their success from day 1. Make games that are simple yet fun for the kids yet have challenging aspects to them to draw in the older crowd. Mario64, for example, is an easy game to beat but getting all 120 stars is a pretty hefty challenge. Luigi's Mansion is again, easy to beat, but finding all the secrets and getting all the treasures and stuff like that is something that only people willing to get good at the game are going to achieve.
There seems to be this worry in the modern day that challenging games will make people lose interest and that's why everything is so fucking easy. Hell, why do you think games like Dark Souls are so popular? It's because they provide a decent challenge that's satisfying when overcome.
DKC is hard as balls and I loved it when I was a kid and I STILL love it now. I feel sorry for this generation of young gamers that have had all the challenge stripped out of every game considered appropriate for their age group.
