I found an odd discrepancy between dungeon difficulty and boss difficulty, which I think explains a lot of the frustration. You can easily go to Carian Castle as your first major dungeon, plow through an easy thread, and then bump into Rellana as your first boss. It happened to me. Then I'm forced to leave because it was impossible, interrupting the natural flow. I went to Belurat, which was much harder as a dungeon, but with a much easier boss.
Then I'm going around Scaldu Altus for a while and end up going to Shadow Mane, having a reasonably hard time, only to be met by Messmer at +7 and get brutalized. I hadn't discovered the Cerulean Coast, so I was underlevelled. I beat him after many tries and changing my build, but it was way harder than the dungeon would have suggested.
Then the ruins of Rhea and Abyssal Woods, and the Mother of Fingers, which are later game, felt much easier, as did everything after Messmer but before the final boss. Bayle was very hard... until you realized that using the Great Dragon Hunter Katana essentially shows he is a gimmick boss ala Rykard. The skill melts him.
The final boss, however, is ridiculous. The first phase is already a bit busted due to the gravity pull attack. But the second phase is simply a mess. The pillars of light make most machines stutter like crazy, but worse still the block visibility to the point you can't tell what animation the boss is loading up, which means you are bound to die instantly.
