I want to know what is the most interesting or important thing in a relationship

According to the experts... The three "C's"... Communication, compromise, and commitment.

I agree and would also add common values as being important.

I also agree on that with you because if one of two is not open to each other, it will only create problems.

communication, emotional stability, sexual compatibility.

I'd go for Complementing one another, Commitment, Communication.
Actually, when the Complementing part is sussed, you can scrap the other two because they then become self-explanatory.

(Want to add that I do not like "compromise". That sounds so negative, as if something is wrong, or that you can't live your life fully when in a relationship. It suggests that when in relationship you cannot have it all. I do not believe that, not when you're with the right person.

Humm for me top of the list is one that connection is there as well as a good sense of humor..

Honesty is a must as well as communication~~~

Some one that realizes we are all different you either accept them for who they are or move on.. You can't change someone, they have to want to change in order to be happy with themselves...

About these 3 Cs... suddenly recalled the ones Matthew Hussey mentions: Chemistry, connection, commitment.
He says the first two don't matter much as you can have either chemistry or connection -or both- with a lot of people. What it comes down to is the commitment.
How he explains it is brilliant, he's got a wonderful metaphor and there's this young woman in the studio who's in a pickle with what she thinks (hopes) is a relationship, but...
If interested, listen to it. Best 31 minutes you'll ever spend on this subject!
http://www.youtube.com/watch?v=uU7hcQwBVoE

Thanks Crystal, I'll watch it in a bit. I tend to agree... commitment seems to be the key for a lot of things. If there's no commitment, there's not much of a chance for relationships to work or anything else you do.