TLDR; Buy this game. It's minimum top 5 all time for me.

I would like to address the negative reviews first:

Look guys, I get your complaints. I experienced what you experienced. I also see that you lack any grit to make it past the 5% mark. I think that is the bigger issue here. I apologize to the developers on their behalf. This is why review ratings lack reliability. However, I can advocate for your concerns as well. IF the developers fully addressed the issues/complaints, what you would have would be GOTY material. As it stands now, I honestly think it has every element in place to fulfill that dream. Just clean up the tid bits and be encouraged that you created something amazing.

I would like to address the Hollow Knight Enthusiasts:

This game is the closest you will get to Hollow Knight. For respect points, I was able to complete all the pantheons with the exception of defeating Absolute Radiance. GAH! However, let me be clear in saying this is definitely NOT Hollow knight. It is comparable in some major elements, but this game draws upon so many other inspirations to the point it stands alone. It could be argued this game is just as difficult as Hollow Knight. The one difference that makes Aeterna easier, is your save points are frequent, and you always have one before each boss/platform segment/etc. I really wish Hollow Knight had this, helps to knock out repetition for fast improvement. Because of this, your skills as a platformer will be unrecognizable after you finish this game. Maybe I can beat Absolute Radiance now lol. Wouldn't that be the ultimate indicator?

My Review:

This game was incredibly difficult and this game could not have been made without at least a hint of sadistic tendencies. You will experience end-game difficulty from start to end. However, there is a way to change the settings at any point to make the challenge easier. I never used it, so I can't say much about it.

There's so much I can say about this game, but a few things stood out for me:
1. Progression in character, mechanics, & skill
2. Exploration & environmental diversity
3. Trials and Rewards

Progression in character, mechanics, & skill
The game does a fantastic job at implementing progression. In the beginning, you are shown as a character who is weak, and is weak. There's not much you can do. By the end, you feel like some kind of Dragonball Z character about ready to destroy a planet. The developers did create a storyline. The concept is interesting, and the way it plays itself into the actual design of the game produces some reeeeally interesting environments. There is also a skill tree, and you essentially earn XP through killing monsters. What you can spend your XP on helps quite a bit with enduring enemies and locations. As for mechanics, you will walk into this game as a naive and soft - fingered baby. When you leave, you will have the hardness of armor on your finger tips, the unfaltering focus and dexterity of a ninja, and the grit of a war-torn gladiator.

Exploration & environmental diversity
Great god this game has the most vibrant and diversified environments of any game I've played. One area you will be underground surround by lava, in another area in the cosmos jumping from one orbital sphere to the next. The monsters fit the profile of these locations and that adds to the diversity. There is also no sense of where you are actually heading off to, in the same sense as Hollow Knight. You just need to explore and where you go is where you go. Eventually you will have the game mapped out and a better sense of areas. The only thing stopping full exploration may be due to requirements in equipment. Also, the game is HUGE. I'm sure the diversity in environment adds to the perception of said hugeness, but holy smokes I cannot understate how big the overall map is.

Trials and Rewards
Along this journey, you gain additional skills and abilities. These skills and abilities are absolutely necessary, and will be used in combination of each other. You cannot progress unless you master the skill and the platforming difficulties that come along with it. There is no forgiveness here either. There were challenges in the beginning that were just as difficult, if not more, than towards the end. Note, I will applaud anyone who can beat this game, but do not expect to be that person. It seems that only 1 in 7.5 people make through the last boss, this does not include other challenges or side quests. I would approach certain challenges and think to myself, "YOU WANT ME TO DO WHAT NOW!? NO EFFING WAY.". Sure enough, I would persevere, my skill would increase, and I would succeed. There was one spot about 60% through the game where I legitimately considered the possibility of defeat. It was a mind-boggling section where I would not blame a single soul for quitting. In return, the game does a tremendous job of rewarding your efforts. Your confidence and perseverance will increase. All items have impact, and nothing is unnecessarily redundant. You will always need coin. Always need health. Skill points are awesome to get, even just one. The dopamine drip this game gives you for succeeding is so, so good.

I could go on, but I wanted to offer a more summary-level review that focused on a few points that impacted me the most. Good luck to anyone considering this game. To those played this game through, congratulations. This was not an easy game.

lots of fun, I wasn't sure at first but glad I stuck with it!

This game starts off as an old flash game, and not in a good way. It's incredibly slow, and neither the controls nor the hitboxes are particularly great. Later on, when you've collected some movement abilities, it becomes at least tolerable in a mediocre way but the controls will always keep it from ever becoming truly good. What I'm saying is there are plenty of far better and more original metroidvanias out there - Spend your time on one of those instead.