To truly get the KH2 experiance, it's best to have beaten COM
Sure, you can play KH2 and understand it just fine, but I don't think you can really get 100% out of the game without having played COM. You get an introduction to The Organization and some of the characters, you will understand the beggining more if you play it as well
I don't get why people don't like COM, or don't think it was fun, I thought it was a great game with an important story, and it's definately worth playing before KH2