Let me preface this by acknowledging this post is heavily opinionated, with MY OPINION, and that I know it will ruffle feathers. However, hopefully this will break the ice and generate more honest, positive critiques here and in other threads. A good, honest critique is valuable and rare. I can be the bad guy to start this off, but I believe we'd all be better served by answers other than "That's awesome!"
Let me also clarify that I am posting as a photographer, not as a reefer. Most of us here are reefers first, who enjoy shooting photographs of our beautiful tanks. There's absolutely nothing wrong with that. Some of us were photographers first, turned reefer, and have a MUCH higher expectation for what's considered a good photograph. However, since this is the Photography forum, it would seem appropriate to dig a little deeper into the details and techniques of photography, and move beyond the dabbling photographer level.
So here goes:
I'm looking first and foremost for a sharp photograph. If it's blurry, it doesn't matter how good the shot could have been, I can't see it. IMO, #3, #9, #16, #21, #27, #29, #37, and #38 are the only ones sharp enough to be moved into the "Let's look a little closer" round. Now I'm looking at composition and lighting. I'll be very frank here, and again preface this as my opinion. Here's what's going through my head:
3: Not bad, really. The eyes are a little blurry, and there are some specks and artifacts that could have been cleaned up. The exposure works for me. Though a little blown out on the edges of the shell, that's to be expected under MH lighting. The subject matter is only mildly interesting, though. Hermit crabs are difficult to make interesting.
9: Nice color on that rose! The coralline and back glass is a little distracting, but that's sure hard to defeat sometimes. I might have cropped it a little tighter to remove these. It's also a little underexposed. Bump it up a little for some "pop!"
16: This one was the first that made me take a closer look, as I worked through the images. Sharpness is real close, and also aimed at the face, which can be a challenge. The photo is a little muddied and dim, which really hides some of the nice highlights that make this photo catch your eye. Composition is a little mug-shot-esque, but it works alright.
21: It's sharp. Look at the eyeball and mouth "hairs." More DOF would have helped this one. I'm not a big fan of macros, though, because of how they're usually just a showcase of "see how close I can get" without consideration made for composition. For me, this CBS just isn't that cool to look at up close.
27: "Oh, so close!" on the sharpening. The only way to make it any sharper would be digital post processing. The balance of the photo is great, I only wish the claw weren't clipped at the bottom. There's no distracting powerheads, coralline, or anything else in the entire photo. There's nothing that assures you this photo wasn't taken in the wild. Bring up the levels in the mouth area (only because the camera can't capture both the mouth and the white anemone at the same time), and this photo is good to go!
29: What an immediate eye catcher! Nice abstract, and I still want to know what it actually is. Harsh direct lighting did some real damage to this one, though. Is this an actual wild shot? If so, awesome catch!
37: Nice photo of a cool behavior. The fish's eye is pretty distracting, though. And the photo is real warm. The shadows also tell me "on board flash" and that necessarily kills any photo for me. There's also a weird haze around the shrimp's tail and legs.
39: The picture's sharp, but that's as far as this goes. The background looks like a concrete wall, there's the on-board flash again, and unfortunately it's a shot of the dirty end of the digestive tract, not the mouth.
So, all that said, #27 for me.