Cool new sprites. You should use more vibrant colors, though. They both look a bit washed out! Did a quick edit on your eye monster for a comparison:
Your eyeball was completely gray. As a general rule, you should never be using true grays in any of your drawings, unless you're going for a very specific effect. In real life, you'll never find any true grays, anywhere. Take a picture of anything (even your eye!) and then do a color picker on it in photoshop or whatever. Unless it's very dark or your camera is broken, you should have some color reflected in there! In cartoony drawings like yours, it's even more important to use colors and lots of contrast, otherwise it'll look depressing and dull. Remember to make your drawings pop. Try weird color combinations! It's better to be a bit oversaturated than to be undersaturated, I think.
Ah, I also gave him some secondary shading from the ground in an attempt to make him look a bit shinier looking. Yours wasn't looking very reflective, in my opinion. Not sure how well I succeeded. Also played around with his iris, giving it a shadow and such. The iris...group...thing bulges off the eye a bit...it's not flat. The cornea is set inside the eye, sort of like a funnel shape? I think, anyway! I advise you to look up eye anatomy, hahah!
Note that my edit isn't too great. But that's because I'm not too great. XD
I'm actually hoping someone else does an eye edit now, so I can see what I did wrong, too. I had a hard time picking decent colors for it, somehow.
Edit: Oh. Just a tip that might be a huge help to you, Bowtie. (It was to me the first time I saw it done!)
Watching a lot of good digital painters do their thing, I noticed a lot of them started by filling their whole canvas with one color - basically whatever color they thought best fit the mood/lighting of their scene. If it was a swamp or a forest or whatever, they'd fill it with a murky green or a happier green, respectively. If it was an airplane battle scene, sky blue, etc. This helps set the mood for your piece, and it helps you paint the objects in your scene better too. Say you were doing the airplane scene. If you started out painting your Red Baron's plane with a simple white background, you might find that when you added the blue sky behind it, it looked too red. Because a red plane in the blue sky shouldn't *be* shaded like a red plane in a white void; the plane in the sky would be picking up the blue light being shot at it from all directions from the sky. It'd end up looking purple in a lot of places!
So when I paint now, I start with a wash for my main color. Then I paint the rough background and such. Then I add in the objects and shade, and keep on adding detail and changing things till they look right. So, when you're making your sprites, it's best to draw them on the background they're going to appear on, so you have an accurate idea of what they're really going to look like. If you don't have a background for them yet, or don't feel like making one, I'd at least suggest putting a wash behind them besides white. The colors surrounding an object dictate what color the object is going to appear as! I drew my eyeball edit assuming he'd be under a cheerful cartoon sky, for example. If he was in a cave, he'd be colored completely differently. Your eye looks weird because you colored him as if he exists inside of a white nothingness, which he obviously doesn't! That makes him look depressing.
Good luck, sir! :3