I see, I understand your motive for removing the ammo now. Then your design philosophy actually quite fits with it being accessible for casuals ie. easy to pick up. It's always good if more people can play and enjoy your game! In that case, I think you can consider simplifying/removing some of your functions to cater towards the more casual spectrum.
For the yellow and blue bar, you should just put a section in a tutorial that talks about it. You can include the yellow bar during the slow time section - maybe you have and I'd have missed it. You should also detail about the blue bar. May I suggest:
For UI improvements, what if you overlay the blue bar over the health bar? So it is more closely analogous to a shield, and when the blue bar runs out, the player starts taking real damage. You can also implement different overlay effects such as shield destruction effects on your screen when taking blue damage, and red blood (or robot blood) effects when taking health damage.
Regarding the slow time - I think you really also just need a better tutorial to showcase what the players can do with slow time. Because I typically only use it to slow time, then just fire at enemies. There is a good GDC talk I recall that says something along the lines of: to have your players do the things you want them to do, you must first teach them. When porting this into a full game - consider only letting the players have limited mechanics before introducing other mechanics as power-ups/upgrades - this will smoothen the learning curve better.
The dive roll is still jenky to say the least. I know you said that you 'needed' it in the second phase of the boss but just as I mentioned - I only needed to sprint around and the boss still wouldn't attack me at all. If you plan to keep the dive roll, you definitely need some enemies that demand the player to dodge it. I think your boss design is good on paper but you just need to fine-tune it to force the player to use dodge roll in order to evade the attacks.
You're on the right track, keep it up!