I'll be honest. Final Fantasy 7 was my first proper RPG and I did struggle with the materia system on my first playthrough. I understood the concept, materia such as 'Fire', 'Restore' and linking them to 'All' was pretty easy to work out. I just struggled with finding effective combination such as utilizing 'Elemental' and 'Added-Effect'.
Also, there were a few boss fights that I was ill-equipped for. This was due to me not knowing their weakness or the fight just taking me totally by surprise. There were a few points where I really struggled on that first playthrough. Bosses like Lost Number, Demon Wall and Rapps (OK, materia not an issue for that one but still hard first time round).
As previously said, after two or three playthroughs you know exactly what you're doing, what materia bosses are susceptible to and how to beat the game comfortably. Maybe if you're on a first playthrough now it would appear easy as gaming has moved on quite a lot in the last 15 years.
But for a 14-year-old, RPG newbie back in 1997. I would say there was plenty of challenge in the game for me.