I had just gotten off of playing some Castlevania: Grimoire of Souls. Since I can wager that this may be the first time that this game has been mentioned on the site, think of it as being Harmony of Despair, but with an actual story.
The long and short of it is that Alucard, under his Genya Arikado alias, is contacted by am order of mages known as the Elgos Order, who have been studying the Grimoire and noticing that the pages have started to become corrupt, with an ominous message saying that Dracula will be revived. Alucard teams up with one of the members of Elgos, Lucy Westenra (yes like the character from the Stoker novel) and her superior [Jack] Seward. After a brush with Death, who easily overpowers the young dhampir, Lucy summons a hero from Castlevania's past: Simon Belmont, the most famous member of the clan. As the story progresses, Alucard and Simon are accompanied by Charlotte Aulin (one of the heroes from Portrait of Ruin), Maria Renard (her young self from Rondo of Blood), and Shanoa (the heroine of Order of Ecclesia), with the ability to call up a support character in the form of Richter Belmont, Jonathan Morris (the main protagonist of PoR), and Maria's adult self (will be added when the game goes public). From what I have read on the Wiki, Trevor "fucking" Belmont (as he appears in Curse of Darkness and the Pachislot titles, rather than the Netflix series) and Albus can be summoned as assists, and Soma can also be played as.
As for why it's "when the game goes public", this is because the game has yet to get an official launch. Currently the game is playable through Canada, although I was able to play it through a workaround app. It seems as though Canada is currently the testing grounds for the mobile market in North America, despite the fact that Castlevania is more popular in the States (in a way, America created the monsters that inspired many of the monsters in Castlevania through the classic horror films)
As for gameplay, it's touchscreen based, with the left side of the screen being for left and right movement, plus dodging, ducking, and dropping through platforms. The right side is for attacks and jumping, with directional flicks for the subweapons and weapon skills. Alucard uses a sword as well as holy water and dagger subweapons. Simon uses a variety of whips, in addition to using daggers, hatchets, and chakrams. Charlotte uses spell books as well as crosses and holy water. Maria uses a variety of birds as her weapon, shares her cross subweapons with Charlotte, as well as the use of cats (which make the Metal Gear "!" sound when they trigger). Shanoa uses the Falcis glyph, manifesting as scythes or lances, shares her cat subweapon with Maria (most likely because she saved some cats in OoE for the Wygol villagers) and makes use of guns as a subweapon (probably to respect Albus and his use of Agathe/Agartha).
As far as levels go, they are (currently) divided into three sets of five levels, with a boss fight at the end, each one based on a different part of Castlevanian history. Chapter 1 is set around the castle itself, basing itself off of the Castlevania 1 version, using the musical tracks of Beginning (Arcade), Vampire Killer (Judgement), and Simon's Theme (Arcade). The first five are set in the woods, the second five are in the courtyard, and the third set are in the main halls. The boss is the Giant Bat (as it appears in Aria of Sorrow before Balore crushed it), with the BGM being "Nothing to Lose" (Arcade). Each section ends with a miniboss fight against a set ammount of enemies, some of them being new, and primarily set to any of the three "Followers of Darkness" or Crucifix Held Close (Arcade). Chapter 2 is set in the City of Haze, with the first set being on the streets with Victorian Fear, the shops with Operation VK, and the subway with Iron Blue Intention, ending with a fight with the Dullahan set to Piercing Silence. Chapter 3 is set in Aljiba during Dracula's attack in Rondo of Blood, with the first set of levels using a new piece of music called "White Noise" set in the woods where Richter fights Death at the beginning of the game, the second set of levels are on the outskirts of town set to Bloody Tears (DXC), and the third set are in the town itself set to Divine Bloodlines (HD), ending with a fight against the Wyvern set against Hellish Hallucinations (or Dancing in Phantasmic Hell/Dark Desires/whatever you wanna call it). Chapter 4, currently the last chapter available, is in the catacombs beneath the castle seen in SotN, using Crystal Teardrops, Abandoned Pit, and Rainbow Cemetery, ending with a fight against Legion, set to Ballad of Death (HD). Upon first defeating Legion, the story throws in a second boss fight against a posessed Soma using the Red Minotaur and Fire Demon souls and set to Dance of Illusions (Judgement). After a short fight, another woman appears named "Hermina" who is revealed to have been a member of Elgos as well, but got too obsessed with the Grimoire, stealing a number of tomes, one of which containing the Dawn of Sorrow bad ending where Soma becomes Dracula reincarnate. Once the game goes public, I can see that the next set of levels are set in the library as seen in OoE, the Chapel as seen in SotN, the lost village from Dawn of Sorrow, and the Clocktower, with a fight against Death set to Dark Holy Man.
The game also has a multiplayer mode called "Bounty Hunt" where you and three other players fight a number of monsters in a confined area, accumulating points until one is declared the winner. If you have made friends in the game, you can team up with them in a Co-Op mode through the main levels.
Thankfully, Konami is learning from the mistakes that EA has contantly made, as there aren't any "Surprise Mechanics", but there is a gacha-like aspect with the "Summon" function. This lets you have a chance at getting new weapons, subweapons, or armor for the characters. If you manage to summon a copy of one such weapon/sub.armor you already have, you can use the parchments that make it up to upgrade the original copy through a "Limit Break," raising its level cap substatially. There is also a trial mode where you can train your characters to get stronger, earn upgrade materials, or earn gold coins to earn either these same materials, stickers (for chatting in Bounty Hunt), or attires (alternate skins). Bounty Coins work in a similar way, but can be earned by playing Bounty Hunt, allowing you to obtain new Konami-themed weapons (Goemon's Gold Pipe (Mystical Ninja), Pentaro (Antarctic Adventure), Salamader Whip, Anubis Rod (Zone of Enders), and the Book of Nemesis (which resembles Vic Viper)
Now I would suggest that you download the app through QooApp if you live outside of Canada, or Google Play/App Store if you live in Canada, as the game is available for both Android and iOS, but only in specified regions. Once it goes public, download the game through your mobile app store of choice.