What, in your opinion, are worthy criteria to be in love with someone?
Whatever criteria you pick, I'm sure it could apply to many besides the object of your desire.
When I read your post, the revised question that popped into my mind was "What are criteria I could use to justify to others (or myself) that my feelings about someone are appropriate?"
Is a "good" reason to be in love really any better than a "bad" reason? I agree with others it's not really something you have a lot of control over. People are complex, and at least for me, sometimes there are reasons I can't comprehend as to why I like someone.
That being said, my experience tells me life is much easier when my heart and my head agree, but it's not always a choice I have.
Now if you change the question to long term compatability traits, maybe that's more along the answers you were looking for.