I think the aspect of WILL is important in this discussion and it wasn’t mentioned yet. At least this is my perception of the issue. Love (in meaning Agape) is for me “a decision and striving towards good of self or another person”. Living in Agape would be a constant exercise of this decision. Positive feelings and sensation of peace and compassion are just by-product. I found some support of this view in concept of neuroplasticity (interesting article is here: http://www.learninginfo.org/neuroplasticity.htm). In short, brain alters its function and structure according to needs. When we are struggling with something our brain gets active and tries to rewire itself to aid us with this task. So as I understand, if we strive to love, it will change its structure and function with time to make it more natural and easy for us. I also found interesting study on monks and compassion meditation (http://www.urbandharma.org/udharma8/monksmed.html).
So, my view would be that love is more related with act of will, and feeling of love and compassion would depend on state of the brain. Some people may feel great helping others (experiencing all-encompassing love while helping one person) and others may just perform action without any stronger reactions. In both ways the love is present and just reaction is different.
Ps. Regarding compassion meditation I tried few types, but the strongest I found was a visualization of sort of hugging inside the heart people who are repulsive, “evil”, to whom we have resentment etc.