I love the idea of Enemy Skill, but it's such a frustrating mixed bag most of the time. There are generally, in all the Final Fantasies with enemy skillls as an ability, one to maybe five good skills that you're actually going to use, and the rest are crap. I mean really just completely worthless. That said, Final Fantasy 7 actually had quite a few quality skills, and relatively few terrible ones. I don't know how many times Enemy Skill materia saved me at the arena. But I usually just use one of the four ES materias on a single character throughout the majority of the game, so it's never a huge focus or anything.