I loved FF7, and I've played 2 and 3 (English numbers). 6 Was one of my favorites, but 7 was also. Part of it stems from delivering the true "epic" rpg experience for me in the bump to 3D. For it's time the game was absolutely incredible. However I can see many branches of animosity.
1.) First FF to appear on a non-Nintendo console. This upset many lol. I know from personal experience.
2.) First FF to "break away" from the "Classic" feel of Final Fantasy games, 1-6 = Flying castles, and knights on Chocobo's etc etc. 7 was very cyber-punk, some liked, some didn't.
3.) People like to toss in the "Cloud was such an emo whiner blah blah blah", yeah umm... when 7 came out, the whole "Emo" thing wasn't exactly popular >_>; Cloud had amnesia, not Manic depression. So 7 is generally referenced poorly in the whole "stereotypical JRPG emo plot ghey POS" list goes on xD. Which also ties into what Montana stated, many people who are a fan of WRPG's will use it as bait to provoke an answer from the FF7 minions.
4.) The milking, the people who already hate the game, probably hate it being used so much. I personally say just don't buy the swag if your not interested, but sometimes you just have to vocalize aggression :)
I will say FF7 wasn't the greatest game of all kind and will forever stay that way, but over-rated is a bit of a long shot. At the time the game was damn near perfect, hell Zelda OOT got better ratings I think >_>; but that's not considered over-rated by any means. I don't see why this should be either.
From 0 to KICKASS in .stupid seconds.
