The Alshich notes that, for someone who should be planning the details of his newly-signed decree to annihilate the Jews, Haman’s reaction is inappropriate, and is therefore another example of H-Shem guiding the behavior of people. H-Shem calmed Haman, giving him the opportunity to make mistakes only blasé, overly confident people make. H-Shem does not control our actions, but He can control our attitudes by removing our worries.
The Vilna Gaon writes that joy refers to physical joy, and a good heart is an internal pleasure.
The M’nos HaLevi writes that the two adjectives refer to two different attitudes simultaneously occurring in Haman’s mind. The first happiness came with his taking pride in the fact that only he was invited to private, royal feast. The other feeling was satisfaction from his meal. This was no mundane emotion, as we know that food has a powerful affect on behavior.
The Kedushas Levi notes that Scripture usually reserves this kind of phraseology of being satisfied for the righteous. Its use here for Haman seems unusual. The Tiferes Shlomo answers with a spiritual answer that the Talmud (Gitin 57b) says that Haman’s descendants learn Torah in Bnei Brak. Considering that Amalek cannot convert, and that Haman’s sons all die, this is indeed strange. Firstly, it is possible Haman’s sons had children before they were killed. As evil as he was, some of the holiness from the meal prepared by Esther rubbed off on him. Holiness never goes away. It can be mishandled, as potential can be ignored.