It wasn't awesome or unique. The only unique mechanic was Astral End, which is barely anything. Ramuh ex, Nidhogg ex, even Seiryu ex all have truly unique mechanics. Zodiark was a massive let down for 10 years of buildup.
I didn't find any of them neat or interesting. Barb was just repeated mechanic vomit coming out really fast and I can't even bother to try Rubi ex. Comparing Endsinger ex to Thordan, Shinryu and Hades, it's clear she's by far the worst.
Tower of Zot was a great dungeon for its difficulty and I did enjoy the trash and bosses, but it's just a dungeon. Most of the other dungeons suck, especially the dungeon leading up to Endsinger.
Both O1s and O5s completely ruined my desire to push any further. Hot cold in O1s was so poorly designed especially for off tanks, and O5s devour was also terribly designed. Neither are even unique. They're not hard, just annoying and anti-fun.
Algaia was okay, but it left me feeling "Oh, THESE are the gods and goddesses we've been referring to since forever? That's it?"
