Visions and Voices/YMMV

Anticlimax Boss: If you don't power it up, the Final Boss is kind of a pushover compared to everything else you've fought. You're automatically healed to full health before fighting it, and though it gets a whopping four attacks per round, the individual attacks don't actually deal that much damage. It's also just as vulnerable to status effects as everything else, and doesn't have a whole lot of tricks up its sleeve.
Crowning Moment of Heartwarming: The Telia and Elena endings.
Crowning Music of Awesome: Pretty much the entire soundtrack, but kind of ruined by the fact that the music titles are all about the innards of a dragon, leading to some rather weird names.
Game Breaker: Vorpal Picks and Void Gems, which cripple enemies' attack stats. There aren't many of them, though, so they usually fall under Too Awesome to Use.
- Dison has an ability that halves the maximum health of an enemy. This works on bosses.
- Lyla. Full-party healing and powerful attacks? You'll likely never take her out of your party.
That One Level: The Organic Tunnels probably count; it's an extremely large and confusing network of fleshy tunnels that's absolutely full of powerful monsters and locked chests.
That One Boss: Silent Alex and the Unspeakables.
- The Netherverse Deity can be difficult too, especially on a solo run, since it has a spell that negates any status effects upon it. This is in a game where status effects are vital to success.
- Hell's Champion. However, this is mainly due to its flunky, Dante's Companion, which gets three attacks per turn, all of which are pretty painful.