Masterpiece and personal favorite.
Graphics/Environment
-Amazing for its time
-Beautiful, enchanting environment
-Immersive story
-Awesome characters
-Brilliant conversations
-Many nice limit breaks and summons
-Cool weapons
-Terrifying ennemies
Gameplay
-More than enough fun mini-games
-Simple equipment/materia system but very effective
-Great variety of materias, which will eventually upgrade if equipped
-Lots of magic materias (everything you can think of...)
-Support materias like All, Quadra Magic, Final Attack, Added Cut, HP Absorb can be linked to magic materias in most pieces of equipment
-Command materias like Deathblow, Double Cut, Mime, Steal and Enemy Skill offers you many options
Sound
-It has the best soundtrack I've ever heard in a game
Difficulty
-Pretty easy even if you're not familiar with RPGs
-Can let the time flow in battle or simply rush the game to increase the difficulty level
-After finishing the game, you'll need plenty of time to grow strong and defeat ultimate weapons
Any real RPG fan must have this game, but I also recommend it to anyone not familiar with RPGs.