Okay, we've reached the halfway save point, so I'll give a few brief thoughts on what's been covered so far. Barret insists on hearing about Sephiroth and the crisis for the Planet while they're all together. I love Barret and Aerith sort of interjecting their thoughts into the story while Cloud was narrating. That's one of those examples of good "normal" character interaction. Makes them seem more real when they're curious and asking questions.
I really like the scene where Cloud talks to his mom, mostly for how he deals with it in the present day. You can tell from his reluctance to talk about it that it's a very painful subject for him. I thought that was a nice touch there. If you go into Tifa's house, she'll ask you questions depending on how much you snoop around. I think you lose affection points the more you snoop around because you invaded her privacy and whatnot. If you play the piano, Cloud will play a bit of the main theme. Remember that for later because if you play it when you get to Nibelheim later on a couple of different occasions, you can get an item from it, including Tifa's Level 4 Limit Break later on in the game.
When we start going through the mountains, they reach a Mako fountain where they start discussing Materia, the knowledge of the Ancients, and magic. Sephiroth goes on a little tangent about how little he respects Hojo, calling him a "walking mass of complexes" and saying he was an inexperienced man given the task of taking over for a scientific genius. It's sort of ironic that he has so little respect for Hojo as a scientist considering he's his father, and without his scientific knowledge, Sephiroth never would have been born as he was.
When you get to the reactor, you find the problem with the monsters appearing is that a tiny little valve is broken. Really, that's it? After the valve is closed, Sephiroth takes a peek into the chambers where the Mako is stored and finds something interesting inside. He tells Cloud/Zack to take a look inside, too, and when he does, he finds a monster smiling at him. He's obviously freaked out about it, and Sephiroth only adds to that sense of shock by telling him these people are humans who have been showered with Mako. This is how real members of SOLDIER are made. Cloud/Zack is different because he's still human.
This prompts Cloud/Zack to ask Sephiroth if that means he's different, too, which sets him off. I really like this scene because it's probably the only part of the game where Sephiroth shows some genuine human emotion. He starts wondering if he's the same as those monsters. He always felt he was different, but not like this. Then a monster breaks out of its chamber and Genesis appears out of nowhere quoting poetry, and...oh whoops wrong game.
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"The great GF...Bahamut."
"...GF? I...? Using my powers...It is you humans...I fear..."