This is surely the sleeper series of this decade. I'm amazed these games aren't more well-known. Let me give you a brief series synopsis, since Google is waaaaaaaay over there. A designer named rdein made a Cave Story love letter game called Momodora, back in 2010 using Game Maker. This is a humble attempt at capturing the magic of those games it draws inspiration from, and it is actually pretty damn solid. Now, taken at face value, the later games are vastly superior, and even CS is superior, but you can tell this guy had a vision, and definitely knew his way around the formula, and genre, and for a first game, he could only go up.
A year later, he made Momodora II. Unlike the arcade-style level progression of the first game, this features a Metroid-esque map system, and focuses more on exploring a world than just beating levels. The camera, mechanics, movement, and physics are also all refined here. It still wears it's Cave Story love on its sleave, but holy hell, these only get better. The sprite work is pretty charming. It's nothing to write home about compared to either sequel, but the cute little characters are full of life, and very well animated, AND very detailed and expressive for being so tiny.
Momodora 3 comes out. It returns to the stage-by-stage design of the first game, but also has some backtracking, and a warp system. This is tied with the 4th game for my favorite. This game, though still very Cave Story like, is really coming into it's own. The combat is better, the item system is better, the controls are tighter, the art is better, the characters are more interesting, and you get to play as two characters (Momo, from the second game, and Dora from the first). Sadly, they do play identically. This game also has an interesting spin on New Game +. It's 2 bucks on Steam, and my best time is 17 minutes (first playthrough was 1:46), so, these aren't terribly long games. The first 2 are free on rdein's website.
Momodora: Reverie Under the Moonlight (Hence fourth referred to as Momodora 4) is the peak of the series. It's like.. If the series came out on NES, this would be the SNES game that Super Mario Worlds the whole series. It takes the art direction to a whole new level, and the sprite work is down right lovable. If you don't instantly fall in love with adorable little Kaho, and get sad every time she squeals when you kill her, there is something wrong with you 
. I can't gush about this game enough. It really revamps the combat from the previous games in a great way. It borrows a lot from Dark Souls. You restore usable items at save points, you have a reusable potion, there's a very well polished, and fun roll/ dodge mechanic, and this is really, for me, the game that shows what this series could become. You have to be smart about combat. Even on normal, you can't just button mash your way through. Some of these bosses are the most interesting since the likes of golden era Castlevania. This is also the longest of the games. It took me around 4 hours on my first blind playthrough, and I got 100%. The world is -probably- about three quarters the size of Super Metroid, but it's hard to guess. It is very much a tried and true Metroidvania with non-linear progression (to an extent) and a huge focus on exploring the world, and finding goodies, new abilities, and health expansions (which you will need cause little Kaho has the stamina of a wet papaer bag).
I don't play a lot of new games, cause I'm really picky. Usually, when I do play a new game, I often beat it once, if at all. I've beaten the 4th one probably five or six times now, and am coming in on close to 10 runs of the third game. I'm serious. If you like Cave Story, Metroid, Castlevania, Zelda, and cute weeaboo shit, then this is seriously the series for you. The 4th, and 3rd games might be my favorite games of this style, besides AM2R, Super Metroid, and Zero Mission. As far as 2D games go, Momo 4 is hands down, my GotY.
So go play them now, if you haven't. Then come back and gush with me.
Oh, these games can be brutal. Just so ya know. A controller is HIGHLY recommended. It's worth getting Joy2Key, or something similar for the first 3. Momo 4 has controller support out of the box, and is 10$ on Steam and PS4, so whats your excuse?
