People have mentioned birds, macros, sports, airplanes, cars, throw in flowers, and then the scenic/landscape shots -- all these things can defy "critique"!
There are a few things that we can discuss, such as "composition", and "technique" -- if I'm going to shoot something and "share" it, I'd hope that I can provide a decent composition and also that I've use a proper technique so that it doesn't come up blurred or with exposure problems, yeah...but then, there are things that aren't so easy to "pick and choose". Take birds (or other wildlife). Unless I'm at a zoo where I can get close to the critters and they are in a pleasing "environment", then a "striking" composition may not be available! And getting good lighting when out in nature, well, sure if we are fortunate, but we so often have to battle with the light!
Sports, well, having the right gear and the proper technique to "grab" the shot and the eye for timing, sure...but how will that come out in the context of "critique" unless it's a group of sports shooters?
Landscapes, yes, composition and yes technique, and certainly an eye for the beauty of nature, and then for example when I was going after shots of some of the local mountains I aimed for the time of day when I could get good light...how boring, though, to look at endless shots of the same old scenes and to try to critique...!
A lot of folks also complain about flower shots. They are common to the point where you could just look away! I will say, though, that a nice flower can be a nice shot because it's showing off the beauty of nature! Given a decent composition and then being able to capture the detail, and having decent light, well there you go, but like I said the shots are common, so what can you say?!
And then there is the whole post-processing thing...many of us would like to believe that our photos are all about the "capture", but let's face it...all of our photos have been "processed", whether in a film darkroom, or in-camera jpeg settings, or in a Raw converter, or by working over in Photoshop or another image editor, one way or another we want to produce images that are visually pleasing not just in the subject matter and composition, but also in how we've handled the tones, the colors, all that stuff!
So, what's my point?
I dunno, I guess first, that we should be aware of all the different things that go into our photography...and then that maybe looking to a big group for "critique" is not the best course! If for example I have some nice shots of flowers (or any sub-category) posting them in the "Critique Corner" may not be my best choice, whereas posting them in either a "flower"/"bird" group may get more useful responses? I don't know, I'm just blabbering on a Saturday afternoon!