Nonsense, eh? From what direction are your little blue fishies lit? Regardless, your shading could use a lot of work, whether or not you choose to admit it. AA is not the problem here. The problem is that relative depth and planes of your sub in particular (though the fishy baddies have it too) are very confusing to the eye. Things that are close to us (like the pods extending from the sides) are shaded exactly the same as things farther away from us (like the fin). Now, it's a good idea to differentiate those planes regardless, but since you're underwater, you don't even need an excuse! There actually WOULD be less detail and contrast in any plane farther from our eyes, even in a photo!
Every surface (save the pod with the 4 lights on it, though the lights obscure it enough for it not to matter) suffers from a lack of color identity, or base hue. Your surfaces consist almost entirely of shadow and highlight, with maybe 10% of your real base hue visible. 50% would be a better number! On top of that, despite insisting on using AA throughout the interior, you've left some very harsh aliasing (especially at 3x) along the windshield edge, where the blue glass meets the green windshield. You need more contrast between your hottest speculars and darkest shadows, but you need to use them LESS overall throughout your sprites.
Of course, I'm sure this is all nonsense. Looks like those soldier types are from...September of last year? It appears that you rejected most people's advice then. I should clarify that the only reason I am offering crits for your underwater scene is that it appears, unlike the other pieces you posted, to be salvageable. It has potential; you have a chance to grow and improve as an artist here if you choose to look at your own work with the same critical eye that you cast on other member's posts.
You've got a good start here, but every part of your picture needs attention. You are capable of doing better work, but it will require time and a critical, analytical mindset. I encourage you to invest a little more, especially in your mockup; it could be the first of many fine pieces from you!