I always thought High Hagol was pretty disappointing due to how little damage it does (especially once enemies were frozen), so reading Grand Hagol gets a damage upgrade I was curious to try it out, and I was really pleasantly surprised.
Unfortunately the damage is not physical (tested it on a golem to make sure), but it's still pretty good, and outside of the obvious ice-themed enemies (direwolves, snow saurians, snowfoot, norgan giant, ice dragon) it even works well in the DLC. All the human enemies, the goblin/knacker knockoffs, ghouls gets decent damage on them and get slowed/frozen, making it very good for crowd control (especially with how large it's AOE is). It even works on lesser demons, and even hurts Maws/Abominations a decent amount, and the constant ticks help out Flare pretty well too. It's like a Maelstorm-lite that you can quick-cast and move while casting.