After playing the other levels and experiencing the rest of the bosses, my full thoughts are this: I think this idea is pretty cool, but needs a bit more time in the oven.
Levels - The Hollow Caves and Tesla Hive levels are pretty fun and simple I find. They can be a bit much at times, but overall not too bad. The Sunken Docks and Doom Gauntlet levels are... A lot. Almost too much even at times. There are a lot of enemies at every corner, to the point of where I just kinda started avoiding them because I was tired of dealing with them. I think having a bit more space or one less enemy here and there would make it feels less cramped and overwhelming.
Bosses -
Globoon The Slime: Having sat with it some more, I think it's fine. I still think slowing him down to be a little slower than the player would be something to at least try and get some more feedback on.
Visage The Golem: He was already discussed on stream, but I'll still leave a little note here. He's the most punishing boss from beginning to end with how he works, giving you only small windows to dodge his stuff effectively. And I don't feel like I should switch suits for anything as if I die, if I wasn't on blue, I'm taking damage immediately. Making it a little looser in the timings and turning the water in phase two into something else would be nice to make it more clear that it's harmful.
Tesla The Wasp: His first two phases are pretty fine and can be kinda fun, if a bit hectic and overwhelming, but upon hitting the third phase... No. I don't like that you can lose access to all platforms at once while still having to dodge the big ball and the adds is just way too much. I think having the platform zaps go in a sequence in phase three would still provide an increase in challenge while also allowing the player to still have full mobility and feel like they're still in control of what to do.
Viklum the Demon?(I kinda forgot and don't wanna go back): He's honestly a pretty fun phase 1. Not too hard, not too easy. Only gripe would be his back-step is not consistent, which makes it hard to judge when and where he's going to stop, leading to some cheap hits. His phase two seems... needlessly difficult to me. His hands just always following you around, making it to where you need the glide suit or the dash suit to deal with them, but even then, I'd prefer that they just had patterns and were part of the attack system rather than their own entities. I'd get some more feedback on that though, it could just be me and I didn't really hang around long to find out.
The Suits - I'll be blunt, I don't know what to make of them. They're all useful in their respective levels, but have no real use case outside of that I find. Maybe more levels would change this? As it stands, I could take them or leave them, but more specifically the dash suit I do have something to say. A part of me kind a wishes that the dash was just an upgrade OR that it didn't replace your attack functions. It's strong, yes, but in the 2nd phase of the boss on that level, it's a complete mixed bag on if it's good or not. I feel like I need the suit to dodge the hands, but that's a trap cause you bounce off whatever enemy you make contact with, meaning you bounce off the boss and right back into the hands sometimes and I have no choice but to play that way if I have the suit on. It's a little restricting.
Weapons - I didn't really test most of them as I got the Pulse Bomb and just used exclusively that for damage. My only real thing with it is I wish you could swap weapons mid stage to encourage the use of at least testing the other ones as I kinda don't want to be without the one I really like if I end up not liking what I picked.
The Secret Challenge Rooms: They're definitely a challenge and can make already pre-existing problems in the level worse as they use the same mechanics and systems, so not really much to say here. Still pretty cool, though.
Anyways, that's enough critiques, I will leave you with the things I really liked: I think the art is well done and super clean, everything looks pretty readable and fun to walk around in. I like the music, it fits well with the game and does encourage me to keep playing if just to listen a little longer. I really do see a lot of promise with the boss fights and would love to try them again after some more tweaks if you continue with this, especially since I really like their designs. They're super cool looking and their attacks are really fun to see in action when I'm not getting pummeled by them. I like the idea of running back through the levels with your other suits to get to new places and find little secrets that could maybe aid you in your endeavors. All in all, I do really like it, I just think it needs a little more refinement to make it that much better. (Sorry if this is a lot, I just wanted to get my thoughts out there. Hopefully my rambling was helpful and not too overwhelming.)