I haven't yet been able to find a complete list of references the Lords of Shadow reboot makes to the older series, the best is a crappy unfinished list in the Castlevania Wiki. I decided to make my own, Am I missing anything?
GABRIEL BELMONT/DRACULA
-David Cox has stated multiple times Gabriel Belmont wears armor which is reminiscent of Simon's artwork and sprite from Castlevania II: Simon's Quest.
-Gabriel Belmont's in game description states he might be the son of one of the nobles of the Cronqvist family, but it has not been proven (Lament of Innocence)
-Gabriel's last name is "Belmont", the last name of the family of vampire slayers since the first Castlevania.
-In Mirror of Fate, you fight Dracula at the end of the game like in most of the previous Castlevania games. His patterns are very similar to the classic Dracula fights including teleportation, flame pillars, and flames from inside his robe/cape.
-He is the master of the castle just like previous games in the franchise.
-In the battle versus the Siege titan seen in the demo of Lords of shadow 2 he quotes the classic line "What is a man... But a miserable pile of secrets!" (Symphony of the night)
-Before his fight with the Forgotten One, Gabriel says the classic line from Symphony of the Night: "Enough talk...! Have at you!"
-In the LOS2 Demo Dracula drinks from a goblet then throws is before doing battle (Symphony of the night)
-In the LOS2 Demo Dracula is waiting for his opponents in his throne room like previous games.
-His sons name is Alucard just like the older games.
-His Castle collapses with his defeat like other castlevanias.
-Subweapons: Holy water and silver daggers as Gabriel.
ENEMY/CHARACTER REMAKES
-Alucard/Trevor
Subweapons/Magic: Bat Form in secret cutscene, Mist Form, Wolf Form, Wings as a double jump mechanism)
(Boomerang/Cross as Trevor) Both Alucard and Trevor had a Stopwatch subweapon.
Both Alucards stories use their mothers as a motivating factor
Alucard is based on Ayami Kojimas design in Symphony of the Night
Notable Appearances: (Symphony of the Night, Draculas Curse)
-Zobek
David Cox has stated Zobek is the Shaft/Death of the LOS universe, In the LOS Epilogue he is seen wearing a purple robe like
the one Death wears. He is also the lord of the dead. Notable Appearances: (Almost every game)
-Carmilla,
Notable Appearances: Circle of the Moon, Simon's Quest
(In the Japanese version of Lords of shadow, Hōko Kuwashima also voiced Shanoa in Order of Ecclesia)
-Cornell
Notable Appearances: (Legacy of Darkness, Judgment)
-Victor Belmont
Notable Appearances: Resurrection (Cancelled)
-Simon Belmont
Based on Ayami Kojimas design in Chronicles for the PS1
Subweapons: Axe and Firebomb like the NES Castevania
Notable Appearances: Castlevania NES, Simon's Quest,Chronicles
-Crow Witch Malphas, (Malphas/Karasuman)Notable Appearances: Symphony of the Night, Dawn of Sorrow
-The Evil Butcher, Notable Appearances: Aria of Sorrow
-Slogra (Background only), Notable Appearances: Super Castlevania 4, Symphony of the Night
-Daemon Lord, Notable Appearances: Aria of Sorrow, Order of Ecclesia
(Might be a Manticore? Notable Appearances: Aria of Sorrow, Dawn of Sorrow)
-Zombie, Notable Appearances: (Almost every game)
-Skeleton Warrior/Armored Skeleton, Notable Appearances: (Almost every game)
-Merman, Notable Appearances: (Almost every game)
-Gargoyle, Notable Appearances: (Bloodlines, Lament of Innocence)
-Giant Bat, Notable Appearances: (Giant Bat, Rondo of Blood)
-Hunchback/Fleaman, Notable Appearances: (Almost every game)
-Harpy, Notable Appearances: (Almost every game)
-Witches, Notable Appearances: (Almost every game)
-Succubus, Notable Appearances: (Symphony of the Night, Lament of Innocence)
-Possessed Armor/Animated Armor ,Notable Appearances: (Almost every game)
-Warg, Notable Appearances: (Symphony of the Night, Dawn of Sorrow)
-Giant Spider, Notable Appearances: (Dracula's Curse, Super Castlevania IV)
-Naiad
(Might be Dead Man's Hand? Notable Appearances: Rondo of blood)
-Cave Troll, Notable Appearances: (Symphony of the Night, Order of Ecclesia)
-Swordmaster
(Might be Vassago? Notable Appearances: Lament of Innocence, Curse of Darkness)
-Mandragora, Notable Appearances: (Aria of Sorrow, Dawn of Sorrow)
-Scarecrow, Notable Appearances: (Symphony of the Night, Harmony of Dissonance)
-Gravedigger, Notable Appearances: (Order of Ecclesia)
-Dracolich Titan
(Might be Death Dragon, Dragon Zombie or, Skull Dragon? Notable Appearances: Legends, Portrait of Ruin, Chronicles)
-Bone Pillar [Immortal,Not on bestiary] Notable Appearances: (Almost every game)
-Puppet/Marionette, Notable Appearances: (Symphony of the Night, Circle of the Moon)
-Magic Tome/Magic Book, Notable Appearances: (Symphony of the Night, Super Castlevania IV)
-Giant
(Might be Balore? Notable Appearances: Aria of Sorrow, Dawn of Sorrow)
-Golem, Notable Appearances: (Almost every game)
-Executioner, Notable Appearances: (Legends, Lament of Innocence)
-Celia (Scroll), Notable Appearances: (Dawn of Sorrow)
-Laura, Notable Appearances: (Rondo of Blood, Portrait of Ruin)
-Olrox, Notable Appearances: (Symphony of the Night)
-Brauner, Notable Appearances: (Portrait of Ruin, Harmony of Despair)
-Medusa/Medusa Heads, Notable Appearances: (Almost every game)
-Walter Bernhard (Scroll), Notable Appearances: (Lament of Innocence)
-Rinaldo Gandolfi, Notable Appearances: (Lament of Innocence)
-The Abbot Dorin, Notable Appearances: (Portrait of Ruin)
-The Forgotten One, Notable Appearances: (Lament of Innocence)
-Sypha Belmont, Notable Appearances: (Dracula's Curse, Symphony of the Night)
-Michael Gelhart Schneider, Notable Appearances: (Castlevania 64)
-Necromancer, Notable Appearances: (Circle of the Moon, Order of Ecclesia)
The heads on the carousel wheel in the Toy Makers Funfair are all references to previous bosses
Medusa, Manticore (According to the Castlevania Wiki), Behemoth, and Maneater
-Grant Danasty (Scroll) His body is found in the Clock Tower same place where he joins Trevor on Draculas Curse.
-Flaming skeleton, Notable Appearances: (Almost every game)
-Iris (Scroll), Notable Appearances: (Rondo of Blood, The Dracula X Chronicles)
RANDOM REFERENCES
The Gloden Paladin in the LOS demo quotes Richter from Symphony of the Night. "Die Monster, You don't belong in this world."
The Music box in chapter 9 plays the theme Vampire Killer.
Veros Woods, and Carmilla Cementary are locations In Simon's Quest.
Wygol is also the name of a village in Order of Ecclesia.
Agharta is the name of Albus's Gun in Order of Ecclesia.
In simons story the entrance cutscene is similar to the entrance in the NES Castlevania. Draculas castle in Lords of Shadow also crumbles when Dracula is Defeated.
The Combat Cross can be used to swing in specific areas like in Super Castlevania 4. The Combos from the combat cross are also similar to the combos in Lament of Innocence as well as the buttons for area and direct attacks.
Due to Rinaldos stake attachment being made specifically for destroying vampires, it gave the Combat Cross the nickname of "Vampire Killer"
If you beat Simons story 100% you get a trophy called "Simons Quest" In Mirror of Fate HD.
You can get a "Tower Key" in Dawn of Sorrow by killing Gergoth.
"Poor, beautiful Carmilla... you will cry bloody tears before this night has ended." - Zobek
Hearts for subweapons, Pot Roast, teleporters, and a map make a comeback in Mirror of Fate
Two toys ressembling old "Death" from previous Castlevania games attack Alucard and he discovers his "Wolf Form"
Using chests to give you more subweapon space and health were also used in Order of Ecclesia.
"Waterfalls of Agharta" is a Remaster of "The Waterfalls" From Super Castlevania 4
You can hear "Ghostly Theatre" in Mirror of Fates "Theatre" if you really listen.