In Resident Evil: Code: Veronica, Alexia Ashford's boss themes are all complemented by soprano vocals, which, understandably had no lyrics in the original Dreamcast release, as all the music was produced with sampled MIDIs. However, in the Darkside Chronicles, which remixes the song, replacing MIDI samples with a real soprano, the song still has no lyrics. This is actually a reference to Alexia herself: the vocals are seemingly human, beautiful, and refined, but on further inspection are inhuman, speaking but not really saying anything - Alexia's human shell covering the monster within.
Another take on Alexia's soprano theme could referencing to the nature of dramatic coloratura soprano in classic operas as well. Most character who is written as dramatic coloratura soprano is either tragic, mad, or evil. The fact that she and Alfred was "created", leads to a tragic fate of both of the twins and their father, as both of the twins succumb into madness. This leads Alexia obsessed to become a mighty queen, a queen who is mad and evil. This is actually a good reference.
I came to a realization that the franchise is not just a horror game series, it's progressed similarly to horror movies that have turned into action flicks, think about it, the first game was like a B-Movie, it had a sequel that introduced darker elements and a coherent story, later had more emphasis on action, as well as remaking the first game to introduce more continuity to be consistent with the sequels, it's like how Evil Dead progressed, in a way.
It always bugged me how inefficient the First Aid spray is. Even the smallest cut or graze requires just as much as a huge gaping wound. Then I remembered how Umbrella originally started life as a legitimate Pharmaceutical company and it hit me — the First Aid spray is the greatest instance of commercialism in the Resident Evil universe and responsible for nearly everything bad that has ever happened. Umbrella had the secret to producing an aerosol capable of regenerating almost any injury, but deliberately designed it so it was both horribly inefficient and horribly expensive; explaining why there are so few cans outside of government and Umbrella facilities — they're the only ones that can buy such an expensive but revolutionary product in bulk. This made them obscenely rich and capable of affording their seemingly endless supply of research facilities and equipment. After Umbrella went bankrupt, the formula to the First Aid spray was bought out by a rival company who kept the inefficiencies but lowered the price enough to give the product mass-market appeal. By Resident Evil 4, the still limited supplies required the Merchant to put on a cap of one spray per customer. By Resident Evil 5 however, the First Aid Spray is cheap and mass-produced on the scale that allows Chris to buy as much of the stuff as he could possibly need.
As a whole, the series has moved away from Survival Horror and become more Actionized because as time goes on the characters are better prepared.
RE 0 and 1: The playable characters have their first encounters with Zombies.
RE 2: Both Leon and Claire are entering Raccoon City for reasons that are unrelated to any zombie fighting. They have also never faced zombies before, but are caught in a local zombie apocalypse.
RE 3: Jill is caught in the middle of RC's local Zombie Apocalypse. She knows about the zombies, but is under equipped.
RE CV: When you gain control of Claire, she has just been released from a prison cell armed with a lighter, and the outbreak is well under way.
RE 4: Leon is sent in to rescue the president's daughter, and is understandably a little paranoid after the events of RE 2. After this, Leon reports back describing exactly what he found out in Spain.
RE Revelations: The playable characters belong to organizations meant to fight all manner of BOWs and the like. Hunters were used in a terrorist attack merely a year before the main events of the game.
RE 5: A black market weapons deal is going on in Kijuju, and the player characters are sent in as backup to stop it. Though initially poorly armed, there is definitely some support infrastructure which is in place to help them out, so they can go to town.
RE 6: The whole world is in danger of getting infected with the C-Virus. The characters are more experienced then ever and actually prepared. Even Sherry Birkin is now able to take down just as many B.O.Ws as Leon or Chris.
It's a little fanwanky, but the membership of the Echo Six squad in Operation Raccoon City could be taken as implicit confirmation that the RE-verse has less restrictions on women in the military, since it features three women in a combat team. That would retroactively remove some of the problems from Jill's background, although it wouldn't help with the age issue.
Why does the knife tend to suck so much in terms of combat against zombies and other various nasties? Because that's how much good a knife would be in a real life situation.
Why does Piers Nivans gain an arm capable of producing electricity when he infects himself with the C-Virus? Because that's what happens when you combine the T- and G-viruses. The C-Virus is made of the t-Veronica virus, a variation of the T-Virus, and the G-Virus variant found in Sherry Birkin's body. Thus, a similar thing could happen, as the t+G virus first appeared in Resident Evil: Dead Aim.
Also, as of why it generates electricity: one of the files in the series mentions that the T-virus destroys cells (causing rot) in order to produce a lot of energy, which is used for the reanimation. The G-virus gives extreme, but hardly controllable, regeneration. Combine the two, and you get a being capable to shoot lighting and able to easily regenerate from wounds and the strain to produce said energy (in fact, mutated Piers can regenerate, and his thunderbolts are Cast from Hit Points). Though, it's an unstable equilibrium: if T prevails, we have a weaker T monster without G regeneration (the tentacled Tyrant); if G prevails, the subject tends to selfdestruct (Duvall).
One of Ada's signature items in the later games is a grappling hook pistol that she uses liberally and in blatant view of pretty much everybody. The single exception to this? RE2, her first appearance, where next to nothing was known about her by any party. How could she possibly have survived that drop into the bottomless pit? Her grappling hook pistol! And she didn't bother to try concealing that she had it afterwards because by that point everyone would have realized she possessed something to that effect in order to be able to walk away from a drop like that.
All of the complicated puzzles found in the series (until Resident Evil 4) are part of the Umbrella Corp's security protocols. Think about it: if your company is developing the deadliest biological agents known to man, you'd want to keep that stuff locked up tight. In order to prevent theft, sabotage, or escape of one of the test subjects, the Umbrella Corp has set up a complex procedure for totally locking/unlocking their facilities, part of which involves that someone be a skilled piano player. In the event that something goes wrong, all of the doors are locked and their keys are secured inside either a puzzle or a specific room. They probably assigned each key/puzzle to a specific person or a select few people so that no single person would fully know how to bypass their security. Fortunately, some of them left clues for others to find in case things went from bad to worse. Guess the Umbrella Corp didn't do a good enough job of screening for employees that wouldn't leak company secrets.
Many have mocked the unnecessary boulder punching in Resident Evil 5, and it may have indeed not been a very practical choice of action. We all know that Chris rightly has issues regarding comrade mortality and during Resident Evil 6, Chris has many, many situations that put his comrades in harm which really stress him out... What does he do whenever one of those situations arise? He hits whatever he perceives as an obstacle. Whether it does any good or not, whether it be an escape pod, metal bars, or a boulder. Turns out it's a bit of a habit for him in desperate situations. What kind of situation was he in when he punched that boulder?
Since injecting himself, Wesker has become nigh indestructible. He evidently does not wish to stick around the mansion when it is set to explode, backs away from his fight with the pyrokinesis-wielding Alexia as soon as he notices Chris is available to do it for him, and is finally destroyed in a volcano. Heck, he even exposes himself to Uroboros, which could be destoyed by pretty much nothing but fire. Kind of a theme going on?
Regarding the volcano, a certain irony that a man who spent his whole life making a mockery of nature and in effect becoming a mockery of nature, was destroyed by one of the most powerful things nature had to offer on the planet he was seeking to infect. (Okay, and rocket launchers, but still).
William Birkin spent the last part of his life working on the G-Virus, insisting that it was his ultimate creation that could bring about a perfect lifeform if Umbrella gave him time to perfect it. Cut to Resident Evil 6 and Sherry, his daughter and the only person to be infected by a controlled, pure form of G, is a (seemingly) unaging human with a powerful Healing Factor and absolutely no negative side effects. By comparison, even Wesker required frequent injections to remain stable. Looks like Umbrella should have listened to their top scientist after all!
It's said outright in the second Wesker's Report that the Arklay mansion lab was in the worst possible place to research the T-Virus, since it was in the middle of a major forest preserve. The original outbreak in the first game thus heavily contaminated the entire forest with a virus that mutates everything it touches into a carnivorous killer. In the various Raccoon City games, it spread into a major metropolitan area and there were mild cases in the city as early as three months before the disaster, which gives it ample time to spread outside of Raccoon. Dead Aim sees a contaminated ocean liner packed with dead and undead T-Virus carriers sink in the middle of the ocean, Darkside Chronicles has an outbreak in rural South America in the middle of the rain forest, and in Revelations, there are still contaminated and potentially lethal T-Abyss mutants washing up on the shores of the Mediterranean Sea a full year after the Terragrigia Panic. Combine that with the multiple listed bioterror outbreaks mentioned in Degeneration, and it becomes obvious that the RE 'verse may not be in the middle of a full-blown zombie apocalypse in the classic style, but they are heading toward a massive mutation that could potentially affect the entire planetary biosphere.
In Resident Evil 2, if you reach the police department without picking up any objects in normal mode, you'll see a zombie in a yellow vest and camouflage pants. This is Brad Vickers. He was the helicopter pilot in the first game. The last time you saw him, he was alive and well.
In the second movie, there is a scene where Jill Valentine and Angela Ashford are hiding from zombified dogs in a school's kitchen. Jill turns on all of the stoves, and runs out with Angela. Awaiting them outside is Alice ready to blow up the gas. This is all fine and dandy until you realize that Alice has no reason to be waiting for them, and certainly no reason to be conveniently smoking the cigarette(Which she got from where?)that she used to blow up the gas. She even has a fireproof blanket to cover up Angela with.