I'm really glad you enjoyed playing the demo!
I wanted to try and come up with unique enemies while keeping a consistent "theme" for each of the planets. Lejra has enemies that try to get in close range while Fabor has enemies that are slow but produce a lot of projectiles. The Trooper is definitely the highest-priority target, it's especially threatening since its speed gets buffed with the wave number, but it also has the lowest HP of all enemies so you can kill it fast.
The demo currently ends after the first planet, but I'm planning for the second and third planets you do in a single run to get tougher with more enemies per wave, new enemy types, and different boss fights at the end. I'm also thinking about increasing the active enemy cap beyond 3 and adding some environmental hazards for later planets, but I'm not 100% sure yet. I'm aiming to make the player's chosen level order much more impactful than it was in Dark Space.
I did try to give Volodiros some extra HP since it's pretty easy to hang around in front of him and pump him full of bullets, but I could increase his HP further or adjust his phase change thresholds if you think he goes down too fast. I do agree that he's the easiest boss of the three, and I also think that his planet is also the easiest one, but I feel like it might be due to the default weapon just being a strong pick there. I imagine Volodiros would be harder to approach with a melee-range weapon.
I did give Karkambian less HP than the other two bosses due to the i-frames in the jumping phases, but he is vulnerable for much less time than normal on Deadly Mode, so that ends up making his fight take a lot longer. There is a bit of a secret strategy you can use against Karkambian to speed the fight up a bit; you can bait him into jumping on the rocks in the corners of the arena, which does a portion of his max HP and stuns him for a little while.
The blue bar will eventually be an energy meter for secondary attacks and buffs on right-click, but there aren't any in the game yet, so it currently doesn't do anything, haha. It (along with the score) will have a purpose in the next version, once I get around to implementing the equivalent of the orbital system from Dark Space.
The next update will be focused on adding new weapons and upgrades. I'm planning for enemies and bosses to drop permanent upgrades that you can manage on the menu to customize your loadout. In particular, Karkambian and Mizerantha will drop alternative weapons (including the fan-favorite snowflakes), Volodiros will drop something that utilizes the blue bar, and the "minibosses" will drop general or weapon-specific augments (for example, the Sand Ghost "orbital" will change the default weapon to shoot two converging bullets like the enemy does). I'm planning to put a hard limit on how many upgrades the player can have equipped at once, but I'm planning for the limit to be able to be raised by reaching certain high score thresholds.