lol. it is a stupid question. if your asking yourself that, somethings wrong.

you want to marry someone that can be your best friend. someone you feel comfortable around. thats what i think.
makes you laugh, holds your secrets, caring, personality/attitude is something you like, respect for each other.

obviously you'll have your differences, everyone does. its not normal if you dont.
one thing that you should have is a good ground base. but what do i know? lol.

i aint married. thats just what i think.

this is a really stupid question, and you all have really stupid answers.

if you're happy then thats the major indicator

I guess you know if you married the right person if you guys get along well, and are able to make each other laugh!

that's a though one, but I think if you start to share the same thoughts as your spouse like you know exactly what they will say or do, then that might be a sign that you understand the person - and might mean that the person is compatible with you. I guess that kinda answers the question.