ff7 had some great gameplay ideas.
Secret characters, great unique personalities like cait-sith, cid, and vincent...special bosses, interesting dialogue, somewhat didn't take itself too seriously but simultaneously had one of the most dramatic moments in all of jrpg history (also the nibelhelm scene).
It was just a really great game.
However, out of the last many, it is also the only one that has not stood the test of time, graphics wise. The polygons are ugly and could be improved in so many ways.
Really, character wise there hasn't been an ff as good since 7. ff8 had a bunch of unlikable characters, 9 was just trying too hard, 10 was really good, but similar problem, 12 is probably the next best after that with balthier and the rabbit lady, though the story-line has too much drama. 13 was meh character wise.
The only other one I'd consider with better characters is tactics.
Anyway, to answer your question, ff7 is just an all-around great game that was always flawed by just a handful of things. This remake gives them a chance to tweak the problems and punch people in the face with nostalgia, as well as make many new fans from the new playstation owners.
