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.
Author's Saving Throw: The developers explained that the reason why Crimson Heads were not included in 0 (after being retroactively introduced in the REmake) is because Rebecca Chambers and Billy Coen don't spent much around the same place as Alpha Team in REmake.
The leech zombies, without a shadow of a doubt. Tough as nails with an insanely long reach, they cause considerable damage when they hit, and when they die, they explode for even more damage. Luckily, fire kills them fairly quickly, mitigating the annoyance a bit.
Eliminators are small, soak up more damage than they have a right to, attack in packs, and like dodging bullets.
Despite the fact she's the focal character of the game, Rebecca is herself one as far as the series itself is concerned. Fans of her were more than pleased to see her get her own game and hope for more in the future.
Evil Is Sexy: The young James Marcus seems to have been invented for the sole purpose of adding more bishonen to the series.
Nintendo Hard: On Hard, this is comparable to Resident Evil: Code: Veronica as the overall lack of ammo and healing items is among the stingiest in the entire series. Unlike that game, however, you do not have a decent knife to help conserve ammo, so you must make every shot count, avoid enemies when possible and only heal when absolutely necessary. If you don't have an excess of ammo for your best weapons and healing items for the final boss battle... forget it. Have fun starting the entire game over!
Scrappy Mechanic: The inventory system often means having to ferry stuff you need from one area to the other.