I think you need more variation in the foreground tiles, because as of now, there's only a few that I see. This is where decay really comes into place, out of the janitor's reach. Maybe have some tunnels dug by escaping prisoners/hungry dragons, attempted tunnels running into something impermeable, and simple smashed bricks. They have a lot of weight on them. And lastly, I'd add some stains, especially near the surface. For one, I don't see any toilets...

If I was one of the scientists, I'd be making bets on whether Robby the rat would survive. Also, on the scientist note, I think there should be a bit of expression- one wincing, one grinning, and one intently watching. Something like that.
If the rings are glowing, the rods should show a bit of a glow around them. Maybe like the edge glow you have with the blue.
When imagining screams, I generally get the picture of people with their tongues drawn in. I'm not sure if this applies to rats, never quite had to deal with them in a long time.

I like the pallet, and the concept is hilarious. I look forward to the final piece

I used a programs anti-aliasing tool on this with inverts from the color wheel. It looks like dark outlines on light colors because of color brilliance. In black and white, even though with the red/green, they have the exact same value/luminance.
To me, there is no solution to blending inverts. I'd go with really smooth splines or lines without anti-aliasing to do this if I had to. Also, if you look closely, the anti-aliasing seems to extrude the circles to the center like buttons. Look closer, and the anti-aliasing is mirrored, so this is just an illusion. Probably due to the brilliance of yellow drawing the eye's focus.
Edit:

If you look at the gradient (cg), the colors go through a colors that look like crap, and which seem darker in the middle.

Never quite done them before, but got a few to do. For now, they are for different strengths of air to ground collisions, and the last is a death animation.
For medium landings (from jump) [Changed in edit 1: less gravity]
For light landings- being knocked back
For heavy landings (fatal). I feel it is way too strong, and if I use it, it will probably be for a desert fatality. Gravity too strong, may use for water impact.
Based off of the above. Forgot to change the eye-white transparency. From Idle animation.
For lighter landings [added in edit 1]
A medium-heavy landing effect, testing dispersing the particles (used cheap transparency). I'm not too pleased with it, but the dispersion looks better. [added in edit 1]
A moderate effect from an attack, seems like a bit of an over kill again. [added in edit 2]
Posted in the order in which I made them. I used the transparency on the first for the dithering, and I do feel guilty about it.
Character, from falling animation. Basically a water balloon.

As these aren't too complex (aside from the pop), I plan to have one for many surfaces and collision levels. I have many more on my to-do list, as I'd like for there to be an effect for every action.
These are all one color for now, and I have no idea how to improve them. My stuff always looks great to me until I know what's wrong, and then like not so. I've seen some really neat pixel art effects, mainly explosions.