Hans Urs von Balthasar defines God's love through the defining of love in general. In his text Retrospective (1988), Balthasar defines love as containing three very important characteristics (or aspects). These aspects are essentially three-fold, mimicking the Christian Trilogy: beauty, goodness, and truth. Through defining the three essential characteristics of love, Balthasar also defines God's love.
Essentially, Balthasar supports this analysis (and his own definition) through the following quote from Love Alone is Creditable.
If God wishes to reveal the love that he harbors for the world, this love has to be something that the world can recognize... [mankind must] have some glimmer of love, some initial sense of what it is.
Therefore, through defining love, Balthasar defines God's love as well. If love is defined as possessing or being beautiful, good, and truthful, God's love is then beautiful, good, and truthful.