So, I applied for the beta and was accepted even though I speak and read zero Japanese. I've been bumbling my way through the game for a bit now. It looks and sounds good (most of the music is just stuff ripped from old games, including Lament of Innocence and Symphony of the Night. The main menu track appears to be original though and is quite good). The presentation is pretty charming, they even have the sprites from the old games running during loading screens and such. The controls of course are pretty wonky. There's some complex swiping motions you have to do in order to use a few special attacks that are on cooldowns, such as Alucard having a multi-hit combo you can do when you swipe left and then down in a certain spot on the screen. It all feels rather awkward to use thus far, and I often find myself not doing the specials when I intend to. Maybe I'd get better at it with practice, but touch screen controls can only do so much. You also seem to bring in teams of characters into missions that you can swap between on the fly. At this point I only have Alucard and Simon. Some of the missions have given me an AI co-op partner, I'm guessing as a stand-in for potential real people down the road.
So far all of the missions are very short bite-sized pieces of gameplay, where you go through simple stages and battle a few enemies to get loot. I've been awarded gold and some kind of red crystal currency for each mission, but I have no idea what these are used for since I can't read anything. There was a bit where I opened a loot box or something, it wasn't super clear, and I got a bunch of various items that it then had me equip on Alucard, so I'm guessing we buy that stuff with the money we unlock (and can probably buy for real world cash, I'd imagine).
Other than that, plenty of typical mobile game stuff. You spend energy to go on missions, and you only have a limited pool of it, which I'm guessing regenerates over time. In theory this will basically force you to play in bite-sized chunks and always come back for more throughout the day. As a Castlevania fan I like all the callbacks to previous games. The artstyle is also great. I'd probably have more fun if I could read anything, and I'll definitely play it more when it's in English.