So, I just cleared out disc 1. Here are my thoughts:
Midgar section is masterfully done.
From Midgar to Junon things are OK. Magic becomes a little underpowered here. Jenova is a challenge, but a good one.
From Costa Del Sol to Corel things are easier than expected. Spells here become almost useless, as they cannot keep up with physical attacks. A boss in Mt. Corel would be nice.
From Gold Saucer to Cosmo Cannon things go smooth. Reno and Rude could have a little more HP. Finally some lvl 2 spells. The Cosmo Cannon section is too easy, as lvl 2 spells level the competition.
Nibelheim and Mt. Nibel were not bad. I'd power up the three guys at the entrance of Shinra Mansion, as they are as easy as a random encounter.
Rocket Town and the Temple of the Ancients were also more easy than expected. The dragon was a pushover. The Demon Wall was most challenging boss since Jenova. Got killed by Beta tough. I didn't saw it coming and hitting for 1500 damage
Yuffie's sequence was surprisingly easy. Rapps was easier than pretty much all random encounters.
Jenofa was the most broken fight ever. I have no clue to how the thing can be killed. I gave up after a dozen game over screens. And while I don't give up much, I got tired of seeing Aeris being impaled with a 5 foot sword by a man who suffers from Buffalo Bill's complex...
As for the whole experience: the mod starts great and kind of dies after Junon. Since levels are earned so fast that kind of takes the edge of make the enemies harder. Also lvl 2 spells felt too cheap. At level 50 Cloud had more than 500 MP, meaning he could cast 34 lvl 2 spells per battle. That's pretty much insane. Takes the challenge out of it. The bosses also stopped posing a challenge after Jenova, Demon Wall being the exception. Gi Nattack was interesting.
My final thoughts: leveling too fast is killing the challenge. I left disc one with Cloud at 55 and I never stopped for leveling up. Summons are too weak. Magic is too cheap. After Junon the mod actually becomes as easy as the original game, mainly because the party is 10 levels above what they would be and spells are cheaper to cast. From Nibelheim onward it just becomes easier than vanilla. I left disc one 15 levels above what I usually do in vanilla.
Now I'm just waiting for the fix to fight Lost Number.
PS: There are two Superballs dropped. The first I don't remember where, but the second is at the fourth fight in Fort Condor.