You've got to be troutting me. ZEMUS? The asshole mentioned in the last five minutes of FFIV and never before that? You're comparing that to a guy who has a constant presence throughout the entirety of FFVII?

It doesn't matter if it was Jenova in Sephiroth's form, it WAS Sephiroth as far as we knew playing through the game for the first time. It was Sephiroth who regularly beat the crap out of Shinra, it was Sephiroth who killed Aerith, it was Sephiroth who broke our main hero's mind and will. The fact he was doing this from a distance is irrelevant because, unlike Zemus and Golbez, the fact Sephiroth was stuck in Northern Crater all this time and he was acting by proxy really changes nothing. The person doing everything in Disk 1 looked like Sephiroth, talked like Sephiroth and was doing what Sephiroth wanted. If it looks like a duck, walks like a duck and wants to commit genocide like a duck....

And yes, I guess you could describe pretty much all the FF Big Bads as "He's crazy, methodical, and cold hearted." I could also describe Light Yagami that way or Naraku or Cell or... Now tell me, is Light Yagami like Kefka? Is Naraku like Kuja? Is Cell like X-Death? The answer of course is no to all of these. Those are stock traits and say nothing of motivations or character background or anything of real substance.

You say Sephiroth was alien but he was the first FF Villain that we actually got to see "fall." The only even vaguely human Big Bads before him were the FFIII Guy and Kefka. So far as I know, their "humanity" comes from a couple lines of dialogues, which is nothing compared to Sephiroth who had one of the best sequences in the game dedicated solely to having us understand him and why he became what he did. It was something completely unique for the franchise at his time and absolutely no one in Shinra has even a quarter as much depth as what we see of Sephiroth in Cloud's Past.

You love your Golbez/Zemus butI'd say a more apt comparison is Garland/Kuja or even Brahne/Kuja. You say Sephiroth did less damage than Shinra? Yes and Kuja did much less damage than Brahne and Garland has done much more damage than both of them. Yet look who's the main villain. Because it's not about who has caused the most direct harm, it's about who is the biggest threat at the moment. Shinra had their time in the sun - a time largely cemented back when Sephiroth was a soldier of theirs by the way - but they're yesterday's news now. Their golden boy, their tool, has decided to go rogue and there's nothing they or anyone else can do about it.

Why do our heroes want him dead Pre-Temple of the Ancients? Well Red XIII only wanted to get to Cosmo Canyon so far as I could tell and going beyond that was because of Bugenhagen. Yuffie is just along to steal our Materia and eventually because she likes us. Cid becomes a fugitive of Shinra so he might as well hang out with Shinra's other fugitives. Vincent is expressly traveling with the party in hopes of meeting Hojo again.

So, no, not everyone in the party is united by their hatred of Sephiroth. But then he summons a planet-ending rock, kills Aerith and pretty much kills Cloud too. That's all the reason the other heroes need now to pursue him. Everyone clearly liked Aerith and one of the best things about her death is the unique animations they all have. Yuffie especially is surprisingly potent as she's the only one who just absolutely breaks down,reminding you she's just a little girl.

I'm not going to tell you Sephiroth is the most unique villain or even anything close to it, but you're dismissive attitude is really annoying. You are purposefully ignoring the game's excellent establishment of his threat. He doesn't need to be on screen kicking a puppy every five minutes, the way people talk about him and the way he's built up, makes the Temple of the Ancients confrontation all the better. It's great that we had seen so little of him up until this point because it meant we weren't sick of him. And you do get sick of Shinra. By the time Scarlet and Heidegger march up in the Proud Cloud, you're just rolling your eyes and saying "will you die already?"

Oh and Barret's arc is one of the best parts of the game. Dyne was a better character than almost anyone you meet in Midgar.