I've never written a critique before, so I hope this is ok. I think it looks really good overall! I can tell you put a lot of work into it, and I think the lighting and colors are beautiful. The stark lighting on the cat really draws the viewer's attention in. The composition is good, but seems a little unbalanced to me; the tubes on the right side feel more full/complex than the tubes on the left, and I think the dark patch in the bottom left corner throws me off a bit. I think my other issue is that I am not quite sure what's going on; initially I wasn't sure whether it took place in space or underwater or somewhere else, though given the name 'space cat' perhaps I can assume it takes place in space? I'm not sure it's communicated clearly (maybe if there were stars in the bg it would read as space more). I think the lighting coming from above also reads as being underwater to me. On the other hand, if it is supposed to be water, I feel like there should be bubbles to show that.
I hope these comments are useful, and that I don't come across as too harsh. ^^