If the intention of the verse is to indicate Achashverosh’s drunkenness, there are simpler ways to say so. According to the Alshich, Achashverosh indeed was not drunk, but simply acting light-headed.
On a deeper, more allegorical level, Rav Yitzchak Hutner (Pachad Yitzchak on Purim) quotes the idea that a mention of a “king” in Megillas Esther also indicates the King of Kings, The Holy One (see our previous blogs regarding this). If so, H-Shem’s “heart” was in a positive spirit because of the distinct behavior of His chosen people.
The Midrash (Esther Rabba 3:11) states that there is no true gratification amongst the nations of the world. Therefore, Achashverosh’s heart wasn’t really gratified with wine, but only seemingly so. In Ohr Chadash, the Maharal asks how this is possible. Do idolators really never experience gratification and joy? It certainly seems they do! He responds that complete gratification only comes from spiritual pleasure, and that can only be achieved through means available only to the spiritual people. Any other gratification is physical and does not have permanence. He quotes as proof the verse in Tehillim (31:20) that promises endless gratification to those who live their lives righteously. As Rav Samson Raphael Hirsch points out in his commentary on that verse, this is a reward in this world, as opposed to the stereotypical suffering tzaddik. In fact, several recent studies demonstrate that people without religion have higher stress levels (read: ungratified) than those following in the ways of Torah (http://www.healthzone.ca/health/newsfeatures/article/1119541–you-docs-having-faith-is-good-for-bodies-and-souls).