Hezbollah and ISIS are two very different entities. While both can be defined as Islamist groups, they have different goals and operate in different ways. One of the primary differences it he scope of focus, with Hezbollah focusing more on its domestic sphere and ISIS focusing much more on a global approach.
Hezbollah is located in Lebanon, and it actually plays a role in the political landscape of that country. Holding many seats in the parliament and trying to bring about policy in line with the group’s Shia goals, the group has used force, but mostly concentrates its efforts on the domestic sphere. Hezbollah has been engaged in a political war to establish Arab dominance in the region, and though it does support some Islamist activities outside of its home country, Hezbollah has a mostly inward looking focus.
This can be contrasted with ISIS, which has a largely outward looking focus. ISIS seeks to establish a wide Islamic state, using Sunni goals and principles. The idea is to establish ISIS as a caliphate, and to expand from there. The group looks at all non-Muslim lands as being potential places for expansion, and there is an element of the ideology that calls for the conquest of non-Muslim people and non-Muslim governments. This group has used terrorism and force outside of its territory, not only directly but through motivating people to carry out attacks in their own way. While Hezbollah is more interested in the domestic environment in which it operates, and it goes about gaining power in much more legitimate ways, ISIS is not concerned with these types of operations. Rather, ISIS is much more concerned with growing its influence around the world in whatever way possible, and is mostly limited in its operations only by its sometimes present financial limitations.
Worrall, James, Simon Mabon, and Gordon Clubb. “Hezbollah, Syria, and ISIS.” Security Issues in the Greater Middle East (2016): 151.