Thank you for playing! There are definitely some issues with enemies that we did not have enough time to fix. They are only bullet-spongy, though, if you're not using the correct weapons against them. Weapons from the future can quickly kill enemies from the past, and weapons from the past quickly kill enemies from the future. This is to encourage weapon switching and ammo management.
When it comes to the glasses, I'm not sure I follow... The glasses give you the ability to time travel, and you need to keep switching timelines to move forward. Some barriers only exist in the past, and some barriers only exist in the future, so you can get around them by time warping while moving forward. The level is pretty linear and doesn't require any backtracking, so if you ever decide to try it again, just move forward and think with time travel!