Good Bad Bugs: The Item Duplication Glitch in the North American version.
Ho Yay: Lots. Just try listening to Leon and Walter's conversations and not pick up subtext.
Magnificent Bastard: Mathias Cronqvist, Dracula's previous identity, counts as one, since he pretends to be bedridden but is actually planning to become the immortal vampire by pulling the strings behind the scenes.
Most Annoying Sound: Walter's "Behold my strength," which he says before unleashing a huge fireball attack. On Crazy Mode, he'll keep doing it until you manage to break the cycle.
Narm Charm: Leon's unforgettably ridiculous outburst to Dracula (after he says that he's beloved and protected by the night) that "I'll kill you and the night!", while absurd, is also considered by many to be awesome too, mostly because it's Kamina's particular flavor of Badass Boast.
The aforementioned Bonus Boss, as well as the general atmosphere of the area leading up to it.
Leon's best friend in the universe, whom he trusted above all else, has betrayed him, used him, and doomed his fiance to a horrible fate, all to become a godless abomination as revenge on God for his own wife's death.
Medusa's frozen expression, face, and overall appearance is quite striking.
That One Attack: Crazy Mode really brings out the worst moves from the final bosses.
Walter's "Behold my strength" attack will now not only blast your health, but he will continue using it until you hit him. The catch? He can use it again before you can reach him, putting you in the blast radius. Unless you have the Wolf's Foot or Invincibility Jar.
Death gains a homing double-attack that he'll start spamming if you are too far away from him (when you hear him yell "Die!" things are gonna suck), Deadly Tempest unleashes two more waves of fire, and there's a new attack, in which Death says "it's over," and throws an energy ball to the center of the stage, resulting in what is basically Demonic Megiddo, nuking the entire screen with an unblockable wave. Good thing you can Perfect Guard!
The final phase against The Forgotten One removes the rocks that protected you from his Breath Weapon in the normal mode, and you can only dodge it with precise movements.
They Wasted a Perfectly Good Character/They Wasted a Perfectly Good Plot: The act that gave birth to the Vampire Killer was Sara Trantoul relinquishing her vampirism-tainted soul to the Whip of Alchemy to unlock its true potential. Though some of this can be excused in that Lament is a prequel taking place at the very beginning of the timeline, this critical plot point is never addressed again in any context. Ever.
Unintentionally Unsympathetic: Yeah, try your best, writers, you are never going to make someone who goes genocidal after his love dies sound sympathetic. Especially if he is instantly ready to give that same emotional damage to his best friend for more or less no reason.