These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Complete Monster: Kagan is the heroine Rayne's Archnemesis Dad and the Big Bad of the second game. A powerful vampire lord, Kagan has a fascination with the Dhampir race and creates his own by raping human women to produce offspring before eventually killing every member of their maternal family and everything they care about, leaving them with nobody but Kagan himself to rely on. Kagan ended up working with the Nazis to further his own goals and killed Rayne's mentor and friend, torturing him by strangling him with his own intestines before the man used a grenade to destroy himself with Kagan, except Kagan had survived. Kagan uses a plan to blot out the sun and leave a vampire kingdom for himself and his kind, to rule as a king. Kagan displays no care for any other being, coldly informing one of his daughters her services are no longer required before having her thrown into a miles-long drop, and later mocks Rayne by declaring she's scarce worth the "effort I took to create it."
Crazy Awesome: Betrayal's final boss is a giant demon that takes up half the screen. Which throws up devil horns during several of its attacks and starts headbanging when it uses its Beam Spam attack after you bring its health down to half.
Game Breaker: The first game's implementation of the Blood Rage mechanic makes Rayne virtually unstoppable. Time slows down, Rayne speeds up, and she inflicts so much damage in such a short amount of time that almost any non-boss enemy will be instantly killed or maimed, and most bosses will have their health drained very quickly. The Bloodlust gauge is also refilled by any melee attack, making it easy to replenish.
Good Bad Bugs: There's a cheat code in BloodRayne 2 that opens up the game's debug menu. This allows you to do things like turn off the bump mapping or screw around with the graphics engine. If you're interested in game design at all, it's actually pretty neat.
That One Boss: The Final Boss battle against Wulf and Beliar is also the hardest. Beliar must be killed within a certain amount of time, or he will grow too large to defeat and instantly kill Rayne via cutscene, and is immune to melee attacks. Wulf, meanwhile, is impervious to bullets, runs at super speed, and has a flame-based attack that can heavily damage Rayne. There are also no lesser enemies in this area to feed upon, meaning that Rayne cannot heal herself during the battle.