I would like to give an illustration as to love versus duty. I think you have already come to some good conclusion as I have read through these posts, but I hope this helps.
Before I give the illustration let me make a few points. First we know from scripture those who say they "love" God yet do not obey him, are deceiving themselves. Love shows itself by action, and it is a motivation. I Corinthians 13 is one of my favorite chapters. This chapter stresses the importance of love being the motivation. Many can be "serving" God, yet, if love is not the motivation, it is for nothing.
I believe love does produce feelings and it is almost impossible to separate love from feeling. I do not believe love is a feeling, but that it involves our feelings. Sometimes love make me sad, sometime love makes me joyful, sometimes love constrains me. For instance if my children disobey me, it makes me sad, because of the love I have for them.
When it comes to our service for the Lord, motivation is VERY important. My service for God needs to be because I love Him.
I have been talking too much, let give my illustration.
Let’s say it is my wedding anniversary and I take my wife out to eat. I then buy her some flowers and a new dress. She then says to me, "Thank you, you really should not have done all this." I then say, "No problem, it was my duty, because it is our anniversary."
My wife would be devastated. She does not want me to do things for her because it is my "duty", but because I take pleasure in pleasing her.
Yet many times in our service for God, Christians serve him only out of a sense of duty. The Lord does not want this any more than my wife does.
God does not want me to serve because it is my "duty", but because I love him and take joy in him. Christians today fail to have their joy in God. Your joy cannot be in God, if love is not the motivation for the service.