I personally find that about 50% if the people who say it's rubbish, haven't actually played it. 3 of my friends dislike the FF series.... until they played it. Surprising isn't it? Many people will dislike it as they go for the "judge a book by it's cover" saying. People don't tend to look within the game or try it out. Many people only play the game either 1: because they've played other Final Fantasies and believed it may be worth a shot at playing. 2: Because they've seen someone else play it and take someones word that it's good regardless or 3: Because they're really bored and looking for a new type of genre/type of game to play. As for the people who do play it and dislike it.
When you've played the game first, it's quite easy to get to grips with the game/storyline as it's like a rollercoaster of emotions. But it really depends on your tastes in the different aspects of the game. For example:
Storyline : Final Fantasy's storylines can hardly be downgraded as they do come up with remarkable ones, but sometimes, the story has hidden pieces and doesnt necessarily tie them all up. It depends on how you look at final fantasy 7's storyline but I find that the storyline is quite remarkable and gripping. As was FF9's.
Graphic Quality : Today is a new day and new technology is being made every second of the day. When you play a game like final fantasy 7 for the first time in this day and age, it doesn't impress you as the graphics are by far poor compared to all the new ff's. Therefore people dislike it because of the quality.
Characters : When you're sat playing a computer game you want to engage a connection with the characters. FF7 does this but still has it's limitations depending on the people who play it. If there's not a character like you, you lose interest, this is the same with the rest of the FF's. As for the enemy characters. You HAVE to have a good enemy to want to defeat. If the enemy doesn't show much evil or power, you think that it's not really worth it. "Too easy". I find that some of the enemies in FF were easy. Other than the Hidden bosses and the End bosses, well again it depends on how you look at it.
Music : The music in the game is highly important in these type of games. I mean, if you played ff7 with no music.. would you want to play it at all? or would you get tired of the silence and emotionless atmosphere? I thought that FF7's music was of good quality and fit in really well with the atmosphere where they were played. But, I have to admit, the other final fantasie's do have some emotional themes which grip the audience alot more than ff7 could.
Battle Sequences : When you're in a battle, you want to feel comfortable with the way you do things, and with the different types of battle combat in all the final fantasies, if you find one that suits you, you tend to adapt to the game and find it alot more interesting, BECAUSE YOU CAN DO IT! lol, anyway. Final fantasy's battle scheme is really good in my opinion as you can choose any character to have certain types of magic rather than one specific character assigned to a job. But some people prefer the job scheme.
Aquiring Skills : Last but not least, as said before, the skills part is quite important too. If you like the job's scheme then you will find that ff7 isn't really going to motivate you as much if you don't like the other area's of it. You fight in battle, you buy materia, you find materia, and you buy/find weapons. Where as in ff8 you had to fight your summons to get them (quite a challenge and really good idea), And in order to learn a certain skill, you had to "absorb" them from enemies or from magic points. These give you a limited amount of usage which imo is rather difficult to manage when you're low on it. As for ff9, you bought a weapon/accessory and with it you had a skill assigned. If you leave the weapon/accessory on long enough while leveling up, you gain that skill and can be used. Unfortunately, that brings difficulty, as you are limited to which skills you use due to the amount of stones you have. The more you level up the more stones you have. Still you can't have them all

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To A Conclusion. You can't really judge people on whether they like or dislike FF7 as it really depends on peoples tastes and expectations of the games. If they dislike one aspect they tend to find flaws in the game and dislike it even more. If people dislike a certain FF then that is only because their tastes are far different to anyone else who loves the game.
I am a big fan of FF7 but I'm torn between all the different aspects of each final fantasy game. Where one game lacks, another game gain's. This is due to the technology and the creative minds which are placed on the square team. Difference will always be there. Without it. Where would we be? In a dull world

. Then there would be no marvelous games such as FF!!! because everyone would be the same, everything would be the same. So be thankful! :P
<3<3<3 Reno mmmmm