Last Epoch is an ARPG with true skill customization.
There are a ton of spells you can learn, though, you can only select a few of them to actually upgrade over time. Every skill has its own individual skill tree, which allows for almost unlimited customization when creating new characters.
For example, the spell above shows a tree where that makes the fire shield do more damage to surrounding enemies. But of course, that's just only one option; there are a ton of other options like increasing shield elemental defense, increasing the radius of which enemies can be burned, and even increasing the number of times where enemies can be caught on fire.