Compassion is a state that is very often misunderstood. There is nothing mawkish or sentimental about true compassion. It is the earnest wish that all beings be freed from their suffering. It can be thought of as an active love, whereas loving-kindness is a passive form. If it is tinged by sadness or pity then it isn't pure.
Sympathetic joy is the wish that all beings continue to enjoy the pleasures they have attained.
This is a somwhat neglected contemplation and many find it difficult to practise. It overcomes the petty-mindedness of jealousy and envy. The near enemy is sensual pleasure and the far enemy is aversion and boredom. Equanimity is the highest and most refined of the divine abidings. It purifies the subtle attachments that the others may still harbour.