1. It managed to run for ten seasons without getting boring.
2. It had non-stop funniness in every episode.
3. When the last episode ended you wanted to cry.
4. You feel like you're one of them.
5. They're not always predictable, unlike some other shows.
6. There's so many different ideas.
7. Their chemistry is GREAT.
8. You think you're going to die laughing at it.
9. You don't care how many times you've already seen each episode.
10. It can be extremely like real life.

This is only ten I can think of many more...