Greetings and salutations!
Today was fairly productive, I feel! To start with, some screenshots showing the current state of the game:
The three powerups thus far implemented--from left to right, I believe: A "spread-fire" weapon, health, and a "charging blast" weapon.
Some of the current state of the game--note the three enemies, the health bar, and the new texture on the level-geometry.
As to specifics, read on:
You may recall that I mentioned in my previous entry that the flying enemy might be scrapped; well, it's working now! It doesn't behave as I had originally intended, but I'm happy with its new (preliminary) behaviour, I do believe. 
Speaking of enemies, they now react visibly to taking damage: they "flinch" a little to one side or the other, may be pushed back by some weapons, and release a quick burst of particles.
Weapons have seen a little work: I have a basic implementation of one weapon's appearance, and an impact-flash for the same.
I had hoped to produce something fancier that I have now--I wanted a 3D model that shaded from bright at its visual centre to darker at the edges, giving a nice, glowy look. I attempted to implement this by looking at the model's normals in the relevant shader, with normals pointing towards the viewer being bright and normals pointing tangential to it being dark. This sort of worked, but not to my satisfaction. 
I also started in on menu-screens today: there is now an incomplete main menu, a possibly-sort-of-complete options menu, and a probably-near-complete credit-text screen.
On a similar note, I selected fonts to use in my UI, including the above-mentioned menus. This took a little searching, especially as I wanted to avoid licences that might be problematic. In the end I found two that I'm reasonably happy with, at least!
I've even made a first step on the in-game UI: as shown above, there's now a simple health bar near the bottom of the screen, which decreases when the player's health drops, and increases when it rises.
Powerups have also been implemented: small red orbs replenish the player's health, while oddly-shaped crystals provide new weapons.
And once again, the game saw various tweaks, changes, and additions that don't seem worth mentioning here!
That then is all for today--stay well, and thank you for reading!
If you want to make it look like the aliens are glowing from the inside, you can place a fake light source in the shader code that computes the length from the light source in object space. Then you can use this term as the light falloff:
That will give a sort-of fake sub-surface-scattering effect.
Anyway, I like how those aliens look. Really freaky.